Be aware when assigning skill points that the max for each of the 4 stats is 10. And when you get the hero upgrade window, it will NOT reflect your artifacts or your spell buffs. For example, you may already have a defense of 10 due to your artifacts, but the upgrade window may only show you have 5 defense. If you assign more points into defense, they will be wasted. I keep track of my hero's 4 main stats on a piece of paper, so when it comes time to upgrade, I won't waste skill points.
The max hero level is 30, so when you get close to that level, be careful where you put skill points.
I always try to get the wall climbing ability soon. It only cost 5 skill points and keeps me from building and dragging around that slow moving wall-bashing equipment. But only your hero can get inside walls. Still, this works well, especially if you are traveling with no other units or with only ranged units. It's well worth 5 points spent. Hope this helps.