Inflate your tires to the max recommended pressure listed on the tire. Even if they don't feel low, you will likely notice a dramatic performance improvement after this.
Every 200 miles or so, clean your chain. This kit cost about $25, but makes cleaning a breeze. Just follow the instructions provided. Alternatively, you can remove your chain and clean it by hand.
Every 100 miles or so, lube your chain by applying a single drop of lube on each link of the chain. This will reduce wear on your chain and improve performance.