I preferred one-handed swords to two-handed swords in Gothic 2, as the faster timing of the swings made it easier to keep pace with and interrupt enemy attack patterns (with two-handed swords I felt like I was getting hit too much due to always being a step being my opponents). Particular fighting techniques vary depending on the enemy you're fighting.
Against less skilled human opponents the best technique is to just alternate between blocking and side-swings. Block-swing-block-swing-etc. Keep up this rhythm and you can beat any low-skilled single human opponent without taking any damage. Skilled human opponents are more difficult as they can perform a quick follow-up attack after you block their initial attack which will get past your block, so against these opponents you just need to be able to take a few hits. Skeletons are the same as humans, with lesser skeletons being like low-skilled humans, and regular skeletons being like skilled humans.
Against goblins the main trick is to not get flanked. Even lone goblins will try to run around behind you, so it's best to just stand in place and turn to follow them, then just quick side-to-side blows the hit them (forward blows tend to just open you up to getting flanked). With packs of goblins the best early tactic is to try to separate them a bit, take out one before the others can get to you, then run away, come back, and repeat the process.
Against many kinds of animals the best tactic is to wait for their charge, then make a quick jump back and follow up with a side swing or a forward swing (depending on the animal). This tactic works well against snappers, lurkers, and dragon snappers (with dragon snappers you can either follow up with a single forward swing, or three consecutive forward swing, the former moving your position slightly backwards overall, and the latter moving your position slightly forward overall).
Other animals, such as wolves, wargs, and field raiders, are best fought by standing your ground, waiting for them to charge, then interrupt their charge with a quick side-swing. With some of these animals they'll try to attack again pretty quickly, so you'll have to keep up your side-to-side swings to match their attacks. The timing can be tricky to master, but is quite effective once you get it down.
A similar strategy works on orcs. Wait for them to charge, then interrupt their charge with a quick side-swing. The orc will then usually move back, try to circle to, and charge again. Keep up the pattern and you can take down an orc even at level 1. Just be careful that the orc doesn't get too close, or they'll start using a rapid side-to-side attack that will kill you very quickly at lower levels. If an orc gets too close just take a few hops back then wait for it to resume its pattern of charge attacks. This tactic also works against lizard men.
Finally, against trolls, you'll want to fight them in the same way that goblins fought you. Charge at them, but then veer off to the side and run behind them. Trolls can't turn fast enough to keep up, so you can keep running behind them while getting in an attack or two as the opportunity presents itself. Like the previous tactic for orcs, this tactic allows even a level 1 character to kill a troll.
Note that all of these tactics are for single opponents- for multiple opponents things get quite a bit trickier, and typically requires being able to take a few hits. Oh, and fighting shadow beasts just sucks, always. No good way I've found to fight them other than just being strong enough to overpower them.
