How difficult it is to level varies per server (low population vs high population), but it also depends on your playing style. Some advice that will help prevent getting ganked:

- Stay away from the obvious gank territories like hillsbrad foothills, STV and tanaris (unless you want to pvp)
- Try to reduce your visibility from roads, etc (if you have a choice, kill the mobs that are furthest away from the roads)
- Watch your chat and combat log for warnings of enemy players(and scout the area where you plan to quest)
- Don't leave a trail of npc corpses (either skip mobs, kill them all on the same spot or skin the corpses)
- Spread your quests over various territories, so you can always go to another territory if your current one turns into a warzone
- Killing other players will usually start your own private war and will probably draw in other (higher level) players, so minimize pvp killing in your quest areas
- If you do kill another player, don't hang around for them to bring in other (higher level) players (preferably go do the quests you have in other regions)

Almost forgot this, make sure that you have a lot of friends that don't mind coming to your rescue when things turn bad. You can mess up all the above, as long as you have enough people that will bail you out.