If you follow these pieces of advice your character will come out well in PVP.
Melee Weapon: Polearm
Not sword, not mace, not daggers. I don't care how unique a snow-flower you are 1v1 you will be better with a Polearm. The only minor challenges you have is the Polearm has a small knockback which can make certain mobile 'exploit spots' challenging.
Magic Lines
Lesser Magic must be brought to 75 to be competitive. The spells unlocked along the way are absolutely key to PVP. Good players will make heavy usage of all three in battles. Not having these spells is equivalent to not having EBOLT in Ultima Online or Life Magic in Acheron's Call:
* Stamina to Health
* Launch (targetted and area effect punt) useful for breaking up lines or propelling yourself over walls
* Heal Self (Heal over Time)
* Heal Other (Heal over Time)
* Lay of Hands (Heal over Time)
Greater Magic needs to be brought ot 50 to be competitive. This means lots and lots of regent farming for Bone which is the easiest way to raise Greater Magic via the ****** and unuseful REND spell (Once you get to 25GM you can cast frailty to gain greater magic. The spell requires 1 sulfur (cheaper) and refreshes much faster than rend. Also, it costs less mana).
Fire Magic
Fire is critical for both PVP and Sieging elements of this game. In particular, Frebolt is one of the few in game means to damagne clan stones. EVERYONE must have this spell.
(thx to bonedancer)