It is all quite simple, its about these things; equipment, spells, and what areas you go to.
First you want to get an equipment setup, you want all your stats maxed(at least the important ones for your classes lvling, plus wisdom, regardless of class wisdom increases the amount of experience you get), always include lvling spells. Then you want to get your hitroll to at least 40, no more than 40 is needed, after you hit 40 hitroll it loses its effects, for example, if you had 120 hitroll it would be no different than if you had 40. Early on this may be a problem, but get it as high as possible while keeping your stats maxed. You only have to get your hitroll to 34, then the bless spell will up it to 40. Now that you have the hitroll, this means you will hit _very_ well. To capitalize on this you want to wield weapons which have high average damage, and have a high proficiency with your class. 75% is usally the lowest in a classes prof. I will take with a certain weapon. You do not need dr on the weapon even, if it has high average damage it will hit more often and harder based on your hitroll/damageroll, so do not take dr over average damage and weapon prof %. The last step is elemental shields, elemental shields do two things, one, they let you get extra hits on mobs, and two they, like melee hits, count for your exp. gaining. So every shield hit will give you exp.
After all of the above is done, you just have to know what and where to kill. You want to have at least two different areas to level in. The rule is, if there is nothing to level off of in the area you are in, then you should not be in the area. Switch constantly between your areas, you want to try to have a constant exp gain. It saves spells and time. You should be moving around all the time, and you are constantly moving through DH and PK Town, so you can easily get fresh spells on your way back to a lvling area. If you are lazy like me you can just log off in a specific area to save spells and wait for repop, its up to you.
Once you hit lvl 45 and you have an alt avatar character you can PVP with it to get quicker easier exp. to lvl 50. Vampires work best for this because they are a fighting class and have a high total exp. at avatar, but any character can be used if you do not have a Vampire. Strip your avatar down to as little equipment as possible, only maxing its str and dex, get your dr as close to 60 as you can while keeping your stats maxed and hr at 40. If you don't have a friend on to help you PVP then you can do it yourself, keep your lvl'ers sanc and eld up and have wimpy on and ld him and hit him with your avatar, don't use sanc or anything else on your avatar but be careful the damage will be intense so be ready to spam heal. Check your lvl'er every so often to make sure they arn't getting too low and heal/sanc them back up.
Weapons with nice average damage; t-blade, fishing pole cut from thick reed, oar, flame lance, neptunes trident, opsrey talon, aurora broadsword, sai, and the best weapon which once you hit 31, you must get this immediatly and use it til av, amazon spear.
Good leveling areas; 1-15, gnomes, newts, CD. 15-40, dag, eg'vane/kotr(got to portal in through blood sea 52w portal to eg'vane) olympus, mithril hall, and some tol. 40-50, tol, olympus, buster bracer/garumn's gorge, tod(this place is good, a little dangerous but worth it.)