L2J Server

I have an question:
Is here any guide about making my own skill effects(changing existing)? I want that to make/fix some new T1(older too) skills on my own. What files i have to change/make, what classes/functions etc.
Thanks for any help/guides/examples for fixing/making ANY skills.

(yeah i know some about skill handlers/xml etc, but i'd be pleased for any help, cause im new in l2j)

Well basicly "all" skills is in XML files and thats all you need. Its pretty simple thou. Of course for some skills (new) there is need for core support too (which is much more complicated to do). Take a look at xml skills files then you will have an idea how this works.

Yeah i know hows XML files work, and how i can "make" skills by that. But i mean these "more complicated" core support.
I discovered that i can make new skills by adding skilltypes in L2Skill.java and register them in GameServer.java and make my own handler ofc.
What more i have to know?

I'll look more in code so maybe i will discover some more, but any "proffesional" guide can be helpful - i can't learn everything on my own.

Regards.

edit: (and how i can edit skills icons and animations? - if its on server side, not client)