It can be hard to browse all the items in the heat of battle. We'll have a guide up eventually that details everything in the shop and favor items eventually, but until then start a game in sandbox mode with an AI opponent and familiarize yourself with what the shop has to offer. You'll want to be able to buy what you need fast and hit the ground running to compete.
An easy tip is to know when to fight and when to run. Make use of teleportation items to escape quickly. There is no glory in fighting to the death. It takes you out of the game for 30 seconds and boosts your enemies gold supply. The game is a series of small battles that make up a war. You don't have to win every battle to win the war.
