This system is to generate skills for characters created at higher than first level, or who increase in level outside normal play.

(1) If the character is being created, first create them at 1st level using the usual Character Generation System. And then...
(2) For each level to be raised above 1st, choose a number of skills equal to INT and give each skill a number of  increases:

The amount of each increase depends skill Difficulty, as per the Experience System: DF1=+5%, DF2=+3%, DF3=+2%, DF4/5=+1%.

The first skill chosen is the "Primary" skill, which gains a full complement of 5 increases automatically. (Usually Defence, gaining +10% per level as DF3. Alternatively Magic or Holiness might be used as the primary,  to create a Mage or Priest of a pre-determined skill-level).

[Also roll for scars etc...?]

CONVERTING CHARACTERS FROM AD&D:

Calculate Decimal Level* = Level + proportion through level due to experience
Calculate Fighting Level* = Decimal Level x 1 for Fighters (inc. Paladins, Rangers)
Decimal Level x 2 / 3 for Clerics (inc. Druids, Monks but not Healers)
Decimal Level x 1 / 3 for Thieves (inc. Assassins, Bards)
Decimal Level x 1 / 6 for Mages (inc. Illusionists, but also Healers)
( * For multi-classed characters, calculate for every class separately and take the maximum. )
Damage Bonus = from Stats Table.
Encumber Maximum = Body Weight x (10 + STR) / 20 (in pounds)
Experience Modifier = INT - 10 per 'class'
Memory Factor = INT / 4 (RETAIN fractions) (applies to Mages only)
Miracle Roll = WIS x 5% (Clerics/Bards only)
Power Factor = WIS / 4 (RETAIN fractions) (applies to Mages and Clerics/Bards)
Agility Bonus = DEX - 10 (?) (Handedness, instead?)
Initiative Modifier = See Stats Table
Size Factor = Derived from Height/Weight and STR/CON (if necessary)
Deaths So Far = Number of deaths character has suffered (if known)
Reaction Bonus = See Stats Table
Maximum Hemchmen = See Stats Table
HIT POINTS = Weight in Stone / 2 (rounded up)
DEFENCE = Decimal Level x 10% + DEX bonus
WEAPON SKILLS = Weapon Base + STR bonus + 10 x Fighting Level + 10 [ only weapons of proficiency]
OR Weapon Base + STR bonus + 5 x (Base Attack Bonus + Proficiency Bonus)
(Use the best value for weapons now in the same Skill Category)
SHIELD (etc) SKILL = Shield Base + STR bonus + 10 x Fighting Level
MAGE
CAST SPELL = INT + Mage Level x 10%
LEARN SPELL = (INT - 5) + Mage Level x 5%
INTENSIFY SPELL = (INT + 5) + Mage Level x 5%
MEMORY = Memory Factor x (Learn / 10*) * Round down after division by 10.
POWER = Power Factor x (Intensify / 10*)
Fetish? Familiar(s)?
CLERIC
HOLINESS = WIS + Cleric Level x 10%
PIETY = Power Factor x (Holiness / 20*) * Round down after division by 20.
Cult Skills - Clerics must have three out of their four cult skills at "Max. Miracle Level" x 20 or more.
THIEF
Sleight (Pick Pockets) = Base (5% + DEX bonus) + 10 + 5 x Level
Devise (Open Locks) = Base (5%) + DEX bonus) + 10 + 5 x Level
Search (Find Traps) = Base (25% + INT bonus) + 10 + 5 x Level
Sneak (Move Silently) = Base (10% + DEX bonus) + 10 + 5 x Level
Hide (Hide in Shadow) = Base (10% + DEX bonus) + 10 + 5 x Level
Climb (Climb Walls) = Base (25% + CON bonus) + 20 + 5 x Level
Backstab :- Number of extra attacks = Sleight / 20, rounded down.
ASSASSIN
As thief, plus...
Poisoning = Base (5% + INT bonus) + 10 + 5 x Level
Disguise = Base (5% + INT bonus) + 10 + 5 x Level
BARD As thief, plus...
Play (Instrument) = Base (0% + DEX bonus) + 10 + 5 x Level
Dancing = Base (?)
Etiquette = Base (?)
Speak Own Language = Language Rating x 25 + INT bonus OR INT x 5
Read/Write Own Script = Language Rating x 20 + INT bonus OR ( INT - 5 ) x 5
Scan (Spot Hidden) = Base (25%) + INT bonus + (Decimal Level - 1) x 5 / 3 [+ any racial/inborn bonuses]
Listen (Hear Noise) = Base (25%) + INT bonus + (Decimal Level - 1) x 5 / 3 [+ any racial/inborn bonuses]
[characters with Hear Noise skill also add the amount by which they have increased it].
Ride = Base (5%) + CON bonus + (Decimal Level - 1) x 5 x Usage Factor*
Swim = Base (15%) + CON bonus + (Decimal Level - 1) x 5 x Usage Factor*
First Aid = Base (10%) + WIS bonus + (Decimal Level - 1) x 5 / 2 x Usage Factor*
Other Language/Script = Language Rating x 20 + INT bonus OR INT x 3
( * Usage Factor = 0 or 1 or 2 depending how suitable the skill is to the known history of the character)
Other Skills - Decimal Level x 10% to divide between suitable skills (+ base + bonuses). [divide by Difficulty Factor]
e (Hide in Shadow) = Base (10% + DEX bonus) + 10

CONVERTING MONSTERS from AD&D

Hit Dice = same 
Hit Points = HD x 5 (if too many for creature size, reduce and give +10% Defence per HD removed)
Armour Points = AC factors due to armour
Defence = 10 x AC factors due to dodging (10% per level for character-types)
Weapon Skills = 20% +5% per HD
Shield Parry (if shield used) = 30% +5% per 2 HD

MAGIC/HOLINESS = 10 + 5 x LEVEL
POWER/PIETY = Magic/Holiness x 0.5 (?)

STRENGTH Bonus = HD - 1
DEXTERITY Bonus = AC (due to dodge) / 2

CONVERTING MONSTERS from D&D 3.x

Special Additions for Characters (quick-and-dirty approximations) :

E.G:

GOBLIN
Goblin, 1st-Level Warrior
Small Humanoid (Goblinoid)
Hit Dice: 1d8+1 (5 hp)
Initiative: +1
Speed: 30 ft. (6 squares)
Armor Class: 15 (+1 size, +1 Dex, +2 leather armor, +1 light shield), touch 12, flat-footed 14
Base Attack/Grapple: +1/–3
Attack: Morningstar +2 melee (1d6) or javelin +3 ranged (1d4)
Full Attack: Morningstar +2 melee (1d6) or javelin +3 ranged (1d4)
Space/Reach: 5 ft./5 ft.
Special Attacks: —
Special Qualities: Darkvision 60 ft.
Saves: Fort +3, Ref +1, Will –1
Abilities: Str 11, Dex 13, Con 12, Int 10, Wis 9, Cha 6
Skills: Hide +5, Listen +2, Move Silently +5, Ride +4, Spot +2
Feats: Alertness
Environment: Temperate plains
Organization: Gang (4–9), band (10–100 plus 100% noncombatants plus 1 3rd-level sergeant per 20 adults and 1 leader of 4th–6th level), warband (10–24 with worg mounts), or tribe (40–400 plus 100% noncombatants plus 1 3rd-level sergeant per 20 adults, 1 or 2 lieutenants of 4th or 5th level, 1 leader of 6th–8th level, 10–24 worgs, and 2–4 dire wolves)
Challenge Rating: 1/3
Treasure: Standard
Alignment: Usually neutral evil
Advancement: By character class
Level Adjustment: +0
A goblin stands 3 to 3-1/2 feet tall and weigh 40 to 45 pounds. Its eyes are usually dull and glazed, varying in color from red to yellow. A goblin’s skin color ranges from yellow through any shade of orange to a deep red; usually all members of a single tribe are about the same color. Goblins wear clothing of dark leather, tending toward drab, soiled-looking colors. Goblins speak Goblin; those with Intelligence scores of 12 or higher also speak Common.
Most goblins encountered outside their homes are warriors; the information in the statistics block is for one of 1st level.
COMBAT
Being bullied by bigger, stronger creatures has taught goblins to exploit what few advantages they have: sheer numbers and malicious ingenuity. The concept of a fair fight is meaningless in their society. They favor ambushes, overwhelming odds, dirty tricks, and any other edge they can devise. 
Goblins have a poor grasp of strategy and are cowardly by nature, tending to flee the field if a battle turns against them. With proper supervision, though, they can implement reasonably complex plans, and in such circumstances their numbers can be a deadly advantage.
Skills: Goblins have a +4 racial bonus on Move Silently and Ride checks. Goblin cavalry (mounted on worgs) usually select the Mounted Combat feat in place of the Alertness feat, which reduces their Spot and Listen check modifiers from +3 to +1.
Challenge Rating: Goblins with levels in NPC classes have a CR equal to their character level –2.
GOBLINS AS CHARACTERS
Goblin characters possess the following racial traits.
— –2 Strength, +2 Dexterity, –2 Charisma.
—Small size: +1 bonus to Armor Class, +1 bonus on attack rolls, +4 bonus on Hide checks, –4 penalty on grapple checks, lifting and carrying limits 3/4 those of Medium characters.
—A goblin’s base land speed is 30 feet.
—Darkvision out to 60 feet.
— +4 racial bonus on Move Silently and Ride checks.
—Automatic Languages: Common, Goblin. Bonus Languages: Draconic, Elven, Giant, Gnoll, Orc.
—Favored Class: Rogue.
The goblin warrior presented here had the following ability scores before racial adjustments: Str 13, Dex 11, Con 12, Int 10, Wis 9, Cha 8.

CONVERTING from RuneQuest (RQ2/RQ3/BRP)

STR = STR ...unless exceptionally strong:  STR 19,20 = 18; 21-25 = 19; 26-29 = 20; 30+ = x2/3. 
INT = INT (component over 18 halved, round down)
WIS = POW (component over 18 halved, round down)
DEX = DEX (component over 18 halved, round down)
CON = CON
CHA = CHA (RQ2) or APP (RQ3/BRP)
Power = POW
SIZ = SIZ ...unless exceptionally large:  Quite Big (8-10ft) = SIZ x 2; Really Big (10ft+) = SIZ x 3. (Otherwise divide height by 3)
Hit Points = SIZ / 2
Armour Points = Average of armour points per location (or according to armour type)
Defence = Defence x2 (RQ2) or Dodge (RQ3/BRP). (Otherwise give 10% per "level" for character-types)
Skills = as given
Magic = Approximate 'Level' of Wizard, then Magic% = Level x 5 + 5   (alternatively, best Sorcery-type skill / 2 ?)
Holiness = Approximate 'Level' of Priest, then Holiness = Level x 5 + 5   (alternatively, highest Allegiance rating / 5 ?)
Spells:
Normal Mage - substitute nearest equivalent Pandarian magical spells.
Normal Priest - substitute most suitable Pandarian religion (and use miracles from that).
Mage/Priest Barbarian - use given RQ spells.
Non-mage/priest Barbarian with significant spells - substitute minor magic item/s (or skills) for the most significant spell/s.
Non-mage/priest Barbarian with minor spells - substitute related skill/s for the most significant spell/s, or just forget 'em.