Once you get the battle tower, about half way through the game, you will be able to reset your skills (for a price). In D2:ED you could reskill about 3 or 4 times, but most people were fine with once or twice their first game (some didn't reskill at all).
If you save before learning new skills you can try them out, and reload if they don't seem helpful. Of course some skills start off useful but get replaced later, or are not that great until they are boosted to higher levels, but you should get a pretty good feel for many skills that way.
There are a couple topics about different builds for D2:ED. Balancing and opponent changes will mean the suggestion there may not be entirely accurate for DKS, but until people play enough to start offering updated build advice...
The official "ULTIMATE MAGE" guide (D2:ED)
So: warrior, mage or archer? (D2:ED)
Character Optimization (D2:ED)
The D2:ED
walkthrough has a skill section with comments, also possibly inaccurate for DKS.