In the beginning if the game, it is important to put your explosives skill up to 30 and your repair up to 30. This way you can disarm the nuclear bomb in megaton and get a house to store you items and whatnot. With the Repair of 30, you can fix the water pipes after you take the unmarked quest from Walter. After the quest he will allow you to collect scrap metal for him. After You have completed those things, Small Guns is the best skill you can put up. Medicine, Lockpick, Repair, and Sneak are the most important skills in Fallout 3.