When a war search is started, can anyone do anything to determine who the matching clan will be? I've noticed the other clan keeps having considerably higher level Town Halls. Step 5 of this wiki how article makes it sound like you can choose who you go to war with
Start wars that you can win. The most important thing about being leader of a clan is managing the clan wars appropriately. If your clan gets smashed, many members will leave and find another clan.