There are a few general questions you can ask yourself which will help show what class you may like:
Do you want to solo or play in a group?
If solo, you can pick anything, but probably not knight or priest primary as they don't typically deal enough damage.
If you want to play in a group, what do you like to do more:
Do you like to heal/help? Then Priest or Druid
Do you like to be able to take a beating/'tank'? Then knight or warden/warrior combo
Do you like to deal damage? Then rogue, warrior, scout, warden or mage
If you like to deal damage:
do you like to be close to your enemy? then rogue, warrior or warden
do you like to be far away? then scout or mage
do you like to attack multiple enemies at the same time? then mage
do you want help from a 'pet' to attack enemies? then warden
Last, what weapons do you think are cool/want to look at constantly?
if a weapon in both hands (and daggers): rogue
if a sword and shield: knight
if a staff: mage, druid or priest
if an axe: warrior or warden
if a bow or crossbow: scout
if two handed swords and axes: warrior or warden
If you just want to be told what to do:
rogue/scout combo (is very popular atm) for physical damage
mage/priest combo for magical damage and survival
Note: races have class restrictions. Both races can pick mage, scout, rogue, or warrior. Elves can choose warden or druid but NOT knight or priest. Humans can choose knight or priest but NOT warden or druid.
Hope this helps. Have fun!