First off, there is nothing wrong with being a bad player & there is nothing wrong with losing. Most people are bad players to begin with, and many people go through long losing streaks.
The big questions are....
Do you feel like you're becoming a better player each time you play?
Do you learn something from each defeat?
Do you keep making the same mistakes?
I didn't win a single game the first 10 times I played 40K, but I always got a little better with each defeat because learned from the experience. One of the most important things to do after losing a battle is to talk with your opponent about it. Ask them what they feel about the game. Did they notice any major mistakes you made? When did they know they had the game? Things like that.
While you can come here and get critical analysis of your army list (which is important for optimizing your army) & how to best play it in general, it's harder for to give more overall general tactical. Things like board set-up, deployment, what to keep in reserve, etc....tend to be things we learn from experience. Sometimes those types of things are harder to recoginize and learn than armylist optimization.