Using sneak helps to reduce unwanted attention. It can be annoying and slow, but until you're used to the place, it helps a lot. Don't wander around at night and stay away from pink spawners.

Listen carefully. Trolls make a distinctive groan/growl that's different from the dwarves, as well as loud stomping feet. You'll usually hear them before you see them. Hit sneak, if you haven't already and try to figure out where they are. It's amazing how those giant blue guys can hide in the forest. If it sees you, run toward the meadows until you can't hear stomping anymore. You will probably pick up a train of dwarves if you do, though. (Assuming you're not up to fighting it yet.)

If you hear the zip of arrows, clanging metal, or rattling bone sound, there are skeletons nearby. They are hostile to dwarves and animals. Skeletons guard towers or crypts. If there's no tower nearby, then there's a crypt. Sometimes crypts are buried in hillsides and hard to see. You will learn to thank the skellies for leading you to them.

If a dwarf is throwing rocks, might as well close in and take care of it before its friends arrive. (Watch out for starred ones though until you get used to them.) Noise attracts attention, and they're easier to kill if they take turns rather than bunching up. Eventually you will get used to the timing of smacking them. Don't just stand still and get hit, run around like they do. Once you're used to them, they're easy to smack. Your third hit does double damage and usually finishes them.

Most common cause of death is forgetting to check your food/health meter before getting into trouble. The first few trips into the forest are the hardest, but soon you'll be wandering around like you own the place, even if you don't upgrade your gear.