If you are new to the game, try to build a balanced group. Taking all DPS classes may make for quick fights, but not in the way that you want it to.
Druids and Mages may seem weak early on, but they can be quite useful.
Not every raid command may be useful for every fight... but, they are all useful for one fight or another.
There is some overlap in loot between various fights, but the odds of finding a particular item may vary quite a bit. If you are having trouble finding gear for a particular class, you may need to try some different raids.
Don't forget about Morale! Not everyone wants to Raid every night of the week. It's useful to give your guild breaks every now and again.
Don't get frustrated if you wipe! A lot of the fights are like puzzles. There's some key to figuring them out. Though, sometimes, you may just need better gear for your raid.
It's only a game! Don't take it too seriously! Have fun! Try different things and remember that you can always load up that saved game!
Keyboard shortcuts:
The F8 Key, or the little blue button on the bottom left of the screen, will open a log of announcements that have occurred.
Ctrl + P will take a screenshot, that should save to the game\data\screenshots sub-folder under where the directory where the game is installed.