Before you put one of these on your weapon, you must make sure the weapon is good enough to spend 100k tokens on. First, you must put it into a category: Relayer or Weapon.
These weapons will generally have resists, HCI/DCI, or other properties that carry over onto equipment other than weapons. See here for properties that apply to relayers. You won't usually find them to be heavy with properties from the Weapon Hits Category, Weapon Hits will only work on weapons used in combat.
Depending on the weapon and play style, the properties you add and extend on your weapon will vary. You'll generally be adding properties from under the Weapon Hits Category of the Weapon Leveling Menu.
The Ideal Weapon will generally have:
Hit Lightning and/or Fireball
Hit Mana Leech
Hit Lower Attack(HLA) and/or Hit Lower Defense(HLD)
HLA/HLD vary - If you have a War Hammer, you'll probably want HLA, as it will help keep you alive longer. A Yumi or other single target DPS(Damage per Second) would want HLD, as you aren't going to get hit and damage is key there.
After these stats, it's mostly preference. Hit Life Leech(HLL) is nice, but dependent on play style. Hit Stam Leech(HSL) CAN be good, but better for Felluca, and especially on a Whirlwind Weapon.
The only time you'll really want AoE on your weapon is if it has Whirlwind. Whirlwind ◊ procs on every target within range, meaning you can hit 9 targets, providing 8 surround you and you are standing on 1. You can proc 9 Lightnings and/or Fireballs and 2-3 Hit Areas, dropping incredible amounts of damage.
You can only gain experience if you yourself kill the monster using the weapon. It won't work if it's by a spell or if your pet kills it (unless the weapon is lvl 50 or above in which case pet kills give 1/8th xp).
All dungeons in Tram and Fel on excelsior have increased spawn. The added spawns in Trammel give less experience (most likely due to the ease of recalling to any area or using the teleporters to get to them). Fel dungeons, however, tend to give more owing to double weapon experience in Fel.
Each time a weapon gains a level, it will gain a certain amount of spending points (aka sp).
Crafted Weapons will gain 3 sp per level.
Artifact & Looted (Non-Crafted) Weapons will gain 5 sp per level.
These points are used to upgrade a weapons properties; Single click on the weapon and select Information, and a gump will pop up.