I've heard plenty of people say playing multiple tables helps them stave off boredom and play more consistently, but for me I start to get distracted if I play more than one or two tables, which usually leads me to play even worse than if I had just been bored of sitting out hands at a single table. So if I find my attention starting to waver, I try to focus more on the hands I'm sitting out, trying to guess what each player has and how they will play the hand. In addition to keeping your mind focused on the game, this technique can also help you get reads on players that you might otherwise miss.