If you’re using SEM as a strategy, you’ll need to test and evaluate your keywords. A good rule of thumb is that for every 100 clicks you get, you’ll get between 3 and 10 enquiries. So, to conduct an efficient test, you’ll want to test around 1,000 clicks. That means setting your budget for Adwords at 1,000 times the cost of the click. If you find that this is going to cost too much, you’ll need to find other keywords or a different marketing strategy.