In terms of how I spend DNA, I look primarily at which creatures I own can be leveled up the most in the future. I’ll eventually go back and try to fill out paddocks but I’m a long way from that point still, so as I progressed through making new hybrids, I only spent DNA on the ones that had the most space to go higher. That gives you the best bang for your buck. But I’ll hatch out pretty much everything else that I get in the game… so I have about half of my common paddocks maxed out now, and starting to get there on some of the rares. I am also at a point where I have enough of a lot of creatures for anything the game throws at me that I don’t level them up until my paddock is filled or close to it, as this greatly improves the DNA rewards from the Code 19s (when we have those to do!) Anything that is good for tournaments I often don’t level up until I have quite a few of, like lvl 20 VIPs, lvl 20 Diplosuchus and lvl 10 of the other super hybrids, etc. You’ll find that leaving these at that level and letting the numbers grow will give you a lot of flexibility in completing tournaments on your own timetable. As I find I have dinos left that I’m not even using in tournaments, I then start moving them up to higher levels.
You also need to be sure to be adding creatures that balance out whatever your top creatures are. So for instance, once a player is adding Indoraptors, the most powerful creature in the game by far, you need creatures at corresponding ferocity to handle the PvEs that you will get as a result. Since the Indo is most challenged against amphibians, that’s why you will often see players at that level with lots of Metriaphodons. But they’ll also often have a bunch of Gorgosuchus (top amphibian in the game) and Segnosuchus (top herbivore hybrid). You would want to constantly evaluate your own teams and adjust what you are adding to both slowly progress your top further, while keeping it in balance in terms of the ferocity and the classes you have.
It all depends on if your goals are more as a collector, or to compete in events and tournaments successfully. But you can of course do both as well, I just put my emphasis more on the former as my focus initially.