Goodmongo has good general advice about how to fight with the starting equipment. Bombs are definitely useful; you should buy the schematic for grapeshot bombs and make a lot of them as they're cheap and make good ranged weapons.
But Goodmongo's skill guide isn't the only viable option. I played Dark mode focusing on the magic skill tree and it was awesome. I like playing for offense so I upgraded Aard and Igni before Quen, but upgraded Quen is also really useful. Prioritize skills that give more Vigor so you can cast more, if you want to try magic. I would still do some sword fighting but I mixed in a lot of signs. The only swordsman skills I took were Feet work 1 and (eventually) Position 1. Position is very useful if you are rolling away from enemies and getting backstabbed a lot. If you're better at avoiding that then it's not critical. Feet work is very useful though since it increases Geralts roll distance and makes it much easier to dodge.
So, don't worry too much about which exact skills you take. More important is fighting technique. As Goodmongo said, try to move in for a few quick strikes and then get out (with a few exceptions... wraiths are easier to kill by attacking constantly and never letting up). Resist the temptation to roll directly away from an enemy (i.e., towards the camera), as this will make Geralt turn his back on the enemy and give them an opportunity for a backstab. Instead, roll to one side to avoid attacks.
When fighting nekkers, be careful not to get surrounded. Dodge away if you are swarmed. Use bombs to hit groups of them. When fighting endregas, be careful to dodge when they charge you (or use Quen, but it will deplete your Quen). Then use heavy attacks. I think endregas are more vulnerable from behind.
Most importantly, though, get the dark gear as soon as you can. It's very expensive, so one way is to fight lots of nekkers without destroying their nests and sell their parts. You can also do arm wrestling at the inn for 30 orens each time, although that gets repetitive quickly. Once you have the Dark equipment things will be much easier. By the time you get to Chapter 2, you'll have good skills too and should have a much easier time. At that point, don't feel like you need to get each new set of Dark gear; there are comparable non-Dark equipment sets late in Chapter 2 and in Chapter 3. But in Chapter 1 you definitely want the Dark gear.
Also, I should point out that for Chapter 2, the Dark mode gear is not only very expensive but also requires a component that can only be found at certain points. On one of the two story paths you can get it at the beginning if you're careful, but on the other path you can't, so you may not be able to craft it until much later in the Chapter. Don't worry too much about saving up cash in Chapter 1 for it though, as you can kill harpies and sell their feathers for a lot of money in Chapter 2. That's a fast way to make money.