First off I would like to say that Monster Kill, or M.Kill, is your friend. What it essentially does is reward you for grinding.
Some people may cringe at the 'grind' word.
You GRIND!? Terrible game! BAD!
Well, so far Cathaal is level 20 and I have been grinding almost exclusively. There is something about Rohan Online that makes grinding not that bad. The devs implemented this great system that lets you take baby steps in terms of XP. Essentially the M.Kill number gives you intermediate goals to look forward to throughout a level. Every 20 mobs you kill a HUGE XP bonus is thrown in your direction.
20th kill = 7 times the XP
40th kill = 10 times the XP
60th kill = 13 times the XP
80th kill = 16 times the XP
100th kill = 19 times the XP
So, while you are leveling you end up looking forward to those huge jumps in XP and will actually seek out a mob that is very hard in order to get the biggest jump possible. Under level 20 you will get as much as half a level or more on your 100th kill.
The funny part is when you are one kill away from getting your M.Kill bonus a bell rings to let you know that the next time you kill something you are getting the bonus so make it count. When that happens I start to salivate.