Regarding Abilities

As far as learning techniques goes there are certain guidelines that need to be followed. There are 'tiers' of techniques that require a certain amount of skill to be able to learn them. To move to these tiers your character will naturally have to increase their abilities in that particular area. I will list below the different tiers your character can ascend and how to increase your abilities within these tiers.

(Note: Hollow/Arrancar are a little special since hollows have no abilities and cannot improve their abilities until becoming Arrancar. However, when they become Arrancar they start off with all Combatant level abilities as their race is naturally inclined towards combat instead of having to learn. Skills also rated in their individual topics with the type and level of mastery needed. All race equivalent skills will be listed as such in their topics.)

Z= Zanjutsu P=Practitioner
Ha=Hakuda C=Combatant
Ho=Hohou E=Expert
Ki=Kidou M=Master

Novice Skill Level: All races start off at this level of ability. There isn't anything you can learn at this tier, it is simply a starting point. Basically a soul.

Practitioner Skill Level: This is basically at the level of someone who is just learning to use their skills but has a bit of practice put in. You are just starting your climb to the pinnacle of ability. The level of an entry level shinigami or normal hollow.
(Requires 10,000 Reiatsu. 25 Str for Zanjutsu/Hakuda, 25 Speed for Hohou, 25 Reiryoku for Kidou. 750 WC to learn.)

Combatant Skill Level: This is someone who has gotten some combat experience and has trained a fair amount in their respective art. They are by no means an expert, but they can certainly hold their own. Roughly at the range of a Vice Captain or Adjuchas class hollow.
(Requires 30,000 Reiatsu. 60 Str for Zanjutsu/Hakuda, 60 Speed for Hohou, 60 Reiryoku for Kidou. 1,500 WC to learn.)

Expert Skill Level: Someone who has reached the level of expert has extensive knowledge in the use of this method of combat and its techniques. They are one of the more talented members of that art form and are something to be feared. At this point you are at the level of an Advanced Vice Captain/Novice Captain or a new Vasto Lorde class hollow.
(Requires 60,000 Reiatsu. 110 Str for Zanjutsu/Hakuda, 110 Speed for Hohou, 110 Reiryoku for Kidou. 2,500 WC to learn.)

Master Skill Level: A true master of their art and someone who has achieved the pinnacle of skill. They are one of the utmost authority in their art and are revered as excellent teachers and even greater warriors. One should be careful before approaching someone who has mastered an art without properly preparing. True power, the level of a Captain or a Vasto Lorde class Arrancar.
(Requires 90,000 Reiatsu. 160 Str for Zanjutsu/Hakuda, 160 Speed for Hohou, 160 Reiryoku for Kidou. 4,000 WC to learn.)