My food doesn't have too much taste / taste allways the same?
I don't know where you are living or the quality of the food you can get your hands on, but these are (obvious) generalities that should be true:


Ingredient quality plays a lot, for example most tomatoes sold in supermarket are just reddish water bags without any taste. You can remedy this either by looking for better quality ones or by adding tomato paste or some kind of tomato concentration. Ground meat, depending on the fat concentration, freshness, etc., can range from fast food leather to deliciousness.
Preparation is something really complicated. Just for the onions there are more than a couple of options for the preparation, did you make your onion sweat? Did you sauté them? When you did add the tomatoes, did you let them reduce and form a sauce? Did add garlic at the very end - the garlic flavor is destroyed really quickly by heat - or if not, did you put enough for it to survive the whole cooking process?
It might just be that you are preparing things in the same "style", hence the impression things are more bland than they might be. Try truly different ones. It might help.
To get really tasty meals, salting is preponderant. However most people underestimate the quantity. By a factor ten or so. Salting at the end of the cooking in the plate is really not ideal too in most meals. You should taste and adjust salt at every step of the preparation. A rule of thumb I heard in kitchen is 10g of salt per kilogram (Measure it in a scale; that's a lot more than what you might think).
Or it is the reverse and it might just be cultural apparatus, used to eat meals heavy on sugar or salt you need time to adapt to the normal taste of things.


As you said the question is really broad, hence the answers are too. Try to understand where the issue comes from by following recipes and then experiment with each factor until you get it right.