hey i have lvled my first aid to 300 on my lvl 50 undead Warlock where should i go to acquire the next recipe/quest to further my skill?

Depending on your faction, a vendor sells the book you are looking for in Hellfire penninsula. I think the cost is 5g and can be found in (edit) falcon watch and the temple of telhammat

As Outlands requires lvl58 to enter solo, have your friends/guild either summon you to Hellfire to purchase the book, or just have 'em pick it up for and pass it your way.

ik heb first aid van 150 en een lv 24

maar ik kan nergens opdaten

http://www.wowwiki.com/First_aid should help you find the next steps you need to advance your first aid skill. It is pretty straightforward.