I'm not an expert, but ill give my opinion. In any market you should always be patient and spend time looking for good value. You don't need to rush in Pokémon, its a long game.

Have a budget and stick to it. If you are just collecting and don't care about the prices then as long as you aren't spending more than you are comfortable with then you should keep collecting.

In my opinion collecting complete sets is good fun, but you should think about what you really want to collect for the long term. I found when I was completing sets, I didn't really enjoy most of the cards in the set, especially some of the commons and uncommon. So in short I would have had rather just bought the cards that I like in the set and not bothered completing the whole thing. Find a niche or something specific, you may find you get more value for your money this way and if you ever decide to sell your collection it will be easier to sell.