Put significant initial skill points into armor user, dodge, and shield user. If you're not into grinding, you can only level them up by repeatedly risking your life in long fights, which has low survivability.
Sneak. Everywhere. You don't want to be seen, and you never know who might be watching. Don't fast travel, you don't want to deal with 7:1 odds in an ambush. Don't recruit companions, they just blow your cover and then get killed. Start every fight on your own terms, with a *sharp* rock to soften up your opponent (never throw the same one twice, knapping builds important skills). You're aiming for broken/chipped bones, which will usually make them pass out from pain in a few rounds. Then, you can move in for a finishing blow, with no risk of being spotted. Even if you are spotted, still be ready to throw if your melee attacks aren't going well -- throwing avoids the usual problems with counter-attacks and parry/dodge. After you level up with thrown sharp rocks, switch to arrows and bolts. They don't break when thrown (you can re-use them), and you can stab with them to perforate enemies (like dragons) that won't even notice a hit from an axe. They honestly seem to do just as much damage thrown as fired from a bow/crossbow, but without the extra hassle of quivers and bows. A thrown corpse or chest full of armor can save your life when things go wrong. Carry a shield (to block attacks) and find a whip as a secondary weapon (they weigh next to nothing, and even a dabbling lasher can easily cripple small- and medium-sized enemies regardless of armor). I prefer axes as primary weapon for their ability to sever annoying body parts like feet/legs (fast enemies), arms/hands (well-armed enemies), and heads (live enemies). If you do bring companions, use them for quests with 1-2 large targets, like night trolls or dragons. They'll dilute the enemy's attacks, and let you finish them off quickly. The companions even usually survive because the fight ends so fast. Make sure they all have pierce/blunt attacks and they will seldom steal your kills.
At this point, your greatest risk is of getting bored. My most recent character hit 100+ notable kills (including vampires, several pairs of night trolls, and a dragon) without taking a scratch, though he did need a couple of companions to take down his first pair of night trolls. Things did get a bit exciting when he entered the wrong dungeon on his third quest and ended up tackling 20+ bandits at once who kept spotting him, but he survived by throwing random objects and ducking around corners to hide.
And yeah, don't get caught outdoors after dark. Bogeymen will shred even a high-level character. Beaches and mountains don't have them, and they don't enter lairs (just make sure to kill the owner first). If you do have to travel in the dark, sneak (never fast travel) and hope...