Hello, in raids there is quite important what role you could play and if you have correct traits and gear and also the order of using your skills (rotation) matters. You can check snowcrows.com webpage to see what builds are actual and which party setup is optimal. So I would start by gearing up 1-2 characters and read some guides of bosses. You can also join the raid training community (link is on the web, depend if you NA/EU).
If you have any other questions, let me know ?