Hi guys,

I know that learning spells increases Magical Aptitude.
Is there some other things that can increase MA too?
Maybe some items: some ring, necklace or robe?

AFAIR Dark Helm is the only item that raises MA, but at the cost of Alignment loss - it's the same effect as Sold Your Soul background.

You can start with a MA bonus of +15 for being an elf, or +5 as a half-elf. There's also the "Sold Your Soul" background option that Kerebron mentioned, as well as a +5 bonus for having "Elven Blood". Just to let the OP know: without Drog's unofficial patch, the Dark Helm is bugged: the bonus is permanent, as is the lost alignment; and if you take it off and put it back on again, those changes stack. The patch fixes this, but also removes the option to use this as an exploit.

Thanks guys.

Every spell known gives you +5% affinity
Racial bonuses actually allow you to go over 100%. So an elf can go up to 115%

It is worth noting that damage with spells scales linearly with your % magical affinity. In multiples of 5%. With 0 and below applying a spell failure chance on cast but having same power as 5%.

100% affinity means you are dealing 20x more damage than 5% affinity.

You only need 2 spells, harm and stone throw (for golems/automatons/objects and other non living things which are immune to harm). But should learn lots of spells as fast as possible to increase your magic affinity as high as possible

The only other viable attack spell is a high level necromancy spell which is extremely inefficient compared to harm, but deals significantly more damage. This matters only if you are using turn based instead of real time. Otherwise you just harm everything to death. With a strong focus on magic affinity you will 1 hit kill most creatures.

In real time you can spam spells, be aware that mana is deducted immediately but the spell is executed after a slight delay

That is, if you have enough mana for 6 spells. clicking the mouse 7 times rapidly will knock you unconscious immediately (from having negative mana) without first shooting the 6 spells. Depending on how fast you clicked, it might not even get a single spell off, just pass out.

As such it is extremely important that you count your clicks and not overspend your mana, ever.
You can also waste spells by casting more than necessary. If an enemy requires 1 spell to kill, you might shoot many more than that at him before the spell takes effect and kills them

It is absolutely imperative that you do not try to balance magic and tech. You should absolutely abstain from one or the other. 100% pure focus in either magic or tech is the only viable option

On a first playthrough. After that, all bets are off; the near-infinite variety of playing options is a big part of what makes this such an enjoyable game.