How do spells improve?

How does it increase in rank and level?

There are two ways to increase the power of the heal self spells.

For starters spells in TL1 fall under either offensive, defensive or charm.
When you level up you can master one of these skills, making it more effective.

If you keep improving mastery in defensive spells then your heal self 1 spell will increase in power as follows:

Health recovery over 4 sec:

Mx1    Mx2  Mx3     Mx4   ...   
141    169  198     226   ...

spells can increase when you train certain attributes (when you level up) or when you learn the next level of the spell.

Another way to increase the power of heal self is to use a higher level scroll to learn the spell. With 'the next level of the spell I mean that there will be scrolls of 'Heal Self 2' (and higher). Each with a minimum level requirement. Once you reach the needed attributes and find (or buy) such a scroll you can erase the old spell from the spell slot and learn the higher level one.

The needed levels for these spells are:

HS1: Level  1+
HS2: Level  7+
HS3: Level 13+
HS4: Level 19+
HS5: Level 25+
HS6: Level 30+