I'm always surprised when authors tell me they don't have a Twitter account. When you finally land your deal, you're going to need a digital platform. The sooner you start building it, the better.
Connect with Agents
Get the inside scoop on pet peeves and common query mistakes by following literary agents on Twitter. Even if you're not looking for an agent, following them will help you discover things that make agents and readers cringe (e.g. starting your novel with someone waking up to an alarm clock, lots of telling in the first few pages).