I usually start out doing all the goodsprings interactions I possibly can, for XP and loot. I also sell of CS items I won't be using for spare caps. I take whatever supplies I can from Doc Mitchell, and do Ghost Town Gunfight. Then I make a trip to the Mojave Outpost (intentionally slow to savor the walk), so I can get a Service Rifle, which I consider the most versatile low-level weapon in the game.