My model building credo is as follows:

1. Have fun

2. Spend the time to learn a new technique (or multiple techniques) with each model. It'll pay off down the road.

3. Experiment freely...you can always repaint.

4. Know when to call a kit finished...I'm very guilty of going back to make improvements all the time.

5. Know your own limits, but try to improve all the time.

6. Respect the history of whatever it is you are building, but don't feel like you need to be completely restricted by it.  I was almost crippled by this at one time...so worried that everything wasn't exactly to spec that I gave up on a kit. I learned that it isn't the end of the world if the mud color you used on that tank is for the Pacific Theatre, not Europe, for example. It matters to some people, but if it doesn't matter much to you, it shouldn't ruin you enjoyment of the hobby.

7. Have fun