Leveling Your Rune knight will be similar to how you leveled your knight mostly mobbing in fields but yet there are some new ways.
You can search over the net for knight leveling guides there are tons available and are very good also.
here is one of the best i have read till date
this will help you in leveling as well as pvp
and for rune knight try those things with new skills magic enchant is very powerful enchant for you with like 60-70 int it will almost double your damage.
A new way to level your rune knight is using death bound the skill of rune knight which take damage then amplifies it by 1500% and returns to the attacker this trick will only work with monster which have melee attack else u will end up dying.
Best place to use death bound will be in Thor's dungeon 3. Get a pasana card in armor and jack card in garment any additional fire proofing if u can get the best it will be. in shield you can try Penomena card.
and you will need lots of white pots / mastela fruits and for SP u can use strawberries they are easily huntable.
take lot of wings too as bow guardian will be a head ache here they are ranged and wont die easy
In the end be careful while leveling this way i have tried and it was worth the exp was good and even if i died i was getting much more then i lost this may not be applicable to server which has exp rate less then 10x but beyond that this trick will rock and if u get too much mob always a fly wing comes handy.
be ware of Ifrit with all the gears he can still toast you in 2-3 attacks