Characters advance by improving their skills - through practice, training or successful experience in the field.

Experience Ticks  When a skill is successfully used in a suitable situation (GM's discretion) the character gains a "tick" for it. Each skill can only have one tick at a time. A character may have up to INT ticks at any one time (but ticks may be discarded in favour of preferred skills).

Experience Rolls  Each tick allows an experience roll to increase the ticked skill. For each experience roll, attempt to roll OVER the skill: each successful experience roll increases the skill by a percentage related to the difficulty of the skill. (These rolls are attempted when there is a convenient break in play, i.e. at the start/end of game sessions, including meal-breaks within extended sessions. Characters are assumed to practice their skills for at least a week after an adventure, or a month or even more for extended adventures).

Experience Maximum  Each character has an Experience Maximum derived from their Intelligence (100-INT). Any experience roll greater than this maximum automatically gains an increase for that skill, even if the current skill percentage is higher.

Heroic Defence (aka Dodge) is the ability which allows heroic characters to avoid damage, injury and death (see the Combat System). Defence increases only by Experience Points awarded by the GM for good role-playing. Each experience point gives +1% to Defence ability automatically, with no experience roll required. Defence ability does not increase in any other way and does not gain ticks for successful use. Defence indicates heroic stature but does not otherwise define abilities: "Experience Level" equals Defence/10.

Experience Points are awarded by the GM for good role-playing. Normally one point is given to all characters at the end of a session (or possibly none/more, if exceptionally pathetic/heroic). "Bonus Experience Points" may be bestowed during play for excellent ideas, saving the party, heroic success, heroic failure, classic characterization, fetching the GM tea, outright bribery or anything the GM sees fit.  Here is a rough guide to the number of experience points that characters may gain in a session:

 
Skill Training and Practice/Research
Characters may also improve skills by training under a Tutor with greater skill. A character must train for a period of weeks equal to the skill Difficulty Rating, and gains an experience tick if the Tutor then successfully makes a skill roll at a penalty equal to the skill of the Pupil.

Training may be obtained from various professional institutions, as well as from private individual tutors (e.g. The Heralds. the Guild of Arcane Lore, the Thieves Guild, various temples and some Mercenary Companies). Tutors are typically about 100% in simple weapon or language skills, or 50% in more complex skills. Usual fees approximate to Tutor Skill x Difficulty Rating sp per week. A Tutor can teach a number of pupils simultaneously, if their combined skill does not exceed that of the tutor. 

Characters may also attempt self-training, known as Practice (or Research for more academic subjects), and the same procedure applies. It is usually much less effective than tutored training, as the Tutor roll will always be 0% (as Tutor = Pupil skill), although any roll of 5% or less counts as success. Costs are one tenth of that for tutored training (for materials, library fees, etcetera).

Characteristic Training
Characters may also increase characteristics (Strength, Wisdom, Dexterity, Constitution, Charisma) by training with specially-skilled professionals (e.g. Heralds/Mercenaries for STR, Players/Thieves Guilds for DEX, Temples/Monasteries for WIS, Alchemist/Apothecaries for CON, Bards for CHA). Each period of training takes approximately 5 weeks (or 1 month) and may include diet and/or exercise. Procedure and cost is similar to that for skills: the tutor must make a skill-roll at a penalty equal to the pupil's characteristic x5, and then the pupil must roll over their current characteristic x5. If successful, the characteristic then increases by 1 point (up to certain limits: STR/CON are limited to the highest of STR/CON/SIZ; DEX/WIS/CHA are limited to one-and-a-half times their original value).

POWER GAIN  Overcoming or resisting the POW of another creature of at least equal Power, usually by magical means, earns the character a Power Gain Roll. When skill-ticks are next checked, roll over current POWx5% to gain +1 POW (Experience Max applies).