Here is the second most common error I find. Outlets without a ground. The problem here I find the most is when there is a grounded (3 prong outlet) in the same room with a non grounded (2 prong) outlet it means often the previous owner just changed the outlets and added a 3 prong outlet but it has no ground. A good home inspector will always find this and point it out to you
The most common issue I find is double tapping. Here you see 2 wires going into a circuit breaker made to only tighten down on one wire. This causes a poor connection on both wires and a major hazard. Make sure you have no double tapped circuit breakers in your panel and if you do call a qualified Electrical contractor.