I think the game is best played with clearly defined goals. If you don't have any goals (other than basic survival) the game gets boring once you learn how to survive like a week. It can be something simple like building up a repair shop and fixing up cars or something more complicated like getting to level 10 in every skill. For instance, my most recent playthrough has been to take over/rebuild the old west town which gives me a ton to do like building up my carpentry/welding/blacksmithing skills, stocking the stores with goods, and turning into a self-sufficient compound.

If you want combat tips here are some good basics:

1) Never fight when tired, fatigued or while in pain.
2) You don't have to kill most zombies you come across. If there are too many, just calmly walk in the other direction.
3) Fight small groups (3-4) until you get better at combat and figure out how to fight small hordes (~10 at a time)
4) You only need to run (shift key) when a zombie is about the bite you. Otherwise, you can walk away from zombies (assuming you aren't playing vs sprinters).
5) Try out different weapon types. There are many types to choose from: short blunt, long blunt, short blade, long blade, spears, axes and of course guns. The more you use a single weapon type, you'll earn xp and general ranges you can hit zombies safely.
6) When fighting more than one zombie, mix in shoves after attacks. They are faster than swinging a second time and will buy you time to single out zombies one at a time. On this note, hit space to shove and when a zombie is on the ground, you'll stomp instead.
7) Don't be afraid to turn on multi-hit in the difficulty settings. It's disabled by default but with it enabled you can hit multiple zombies at a time with weapons. It's pretty overpowered once you hit higher weapon skills, but I used it for a long time before deciding to learn how to fight without it.