To prepare your pet for the Battledome there are three things you must do:  raise its statistics, acquire abilities for it, and purchase some weapons.

The most common way to increase your pet's statistics is to take courses at the Training School at Mystery Island or the Academy at Krawk Island.  Tuition at the Training School is paid with codestones, at the Academy with Dubloons.  The number of codestones or dubloons depends on the Level of your pet.  Until your pet reaches Level 20 it is less expensive to train it at the Academy.

Codestones can be found in user shops, auctions, and the trading post.  They also sometimes appear in random events and as prizes at the Tombola and Coltzan's Shrine.  Dubloons can be found in user shops, auctions, and the trading post.  They also sometimes appear as prizes at Coltzan's Shrine and the Buried Treasure game.

There are other ways to increase your pet's statistics.  One free way is to visit Coltzan's Shrine in the Lost Desert every day.  It doesn't give statistics every time, but quite often.

The random faerie quests (except for the Earth Faerie) usually increase one of your pet's statistics.  Some games occasionally give random statistics.  A rather expensive way to increase statistics is to feed your pet certain types of neggs.

Another quite expensive way to increase your pet's statistics (although if you're going to get into battling big time it may be cheaper in the long run) is to assemble the nine pieces of the Secret Laboratory Map to gain once-a-day access to the secret lab.  The secret lab will raise or lower your pet's statistics at random, but in the long run they will increase.  The lab may also change your pet's color, species or gender.  For an 8 month record of one pet's results at the secret lab, go to this pet page.  At this time it will cost around 360,000NP to get all the map pieces.

The statistics that matter in the battledome are health points (endurance), strength, and defense.  Level is important in that it determines how far you can train in the other statistics.  Move (agility) and intelligence are of no importance in the Battledome at this time.

Your pet receives abilities from bottled faeries (Earth, Water, Air, Light, Dark, and Fire).  Each faerie has a number of abilties that it grants.  Your pet must be at a certain Level to receive each ability and they are granted in a certain order.  A higher ability won't be granted before you have received the previous abilities, even if your pet is at the required Level.  If you pet is not at the required level to receive the next ability of a particular faerie, the faerie will just fly away and your neopoints will have been wasted.  For a chart of faerie abilities and the level your pet must be to receive them go here.

Unfortunately, many abilities are not much use in the Battledome.  The most desirable abilities are Burrow (4th Earth Faerie ability, Level 10), Drain Life (7th Dark Faerie ability, Level 21), and Sink (8th Dark Faerie ability, Level 30).

Bottled faeries can be purchased at the Battle Magic Shop (on the second central shops map) and in user shops, auctions and Trading Post lots.  They also sometimes appear in random events and as prizes at the Tombola.

This site cannot begin to explain all you need to know about weapons, but there is a wonderful site that you must bookmark and refer to often to guide you in your choice of weapons.  It is PinkPoogleToy's In Depth Battlepedia.  It has much more detailed information about weapons than the Neopets battlepedia, including ratings by players who have used them.  You will also find a lot of other valuable information relating to the Battledome there.

A few things to keep in mind relating to weapons:

• Some weapons can only be used by a specific species of pet.
  
• Some weapons are offensive, some are defensive, and some are a combination.
  
• Some weapons can only be used once and are gone, some can be used only once per battle, and some are breakable (gone for good) or semi-breakable (gone for the battle).
  
• Some "weapons" are actually healing items that can restore your pet's health points during a battle.  (This does not include Healing Potions, which cannot be used in the Battledome.)