A few things:
-don't trust anyone
-always have two of everything (food, water, bandages, etc.)
-avoid major cities for the early part of the game. They offer great loot but are filled with heavily armed players who will kill you.
-when you pull zombies, find a nearby hill before shooting them. Zombies are slowed down a lot by hills.
-if you're in a city when you pull zombies, find a building. Zombies slow down entering buildings.
-If you pick up a rifle, don't use it unless you absolutely have to. The sound draws zombies from all over.
-probably self-explanatory, but always crouch when you see zombies.
-generally just stick to scavenging smaller towns and buildings early on. They're safer and offer good loot to start things off.
-If you get a compass, always go north.