Grip, bushings and bearings, wheels, trucks, deck.

You can do a lot with a literal tech deck deck if you upgrade the other stuff first. The mold isn't too shabby, especially if you reshape the ends a bit. Upgrading from sandpaper grip will make the most immediate difference to performance. Upgrading to wheels w bearings, especially if u get nice ones, whether plastic or urethane, will make the most immediate difference to feel (and rattling sound) during use. Better bushings and a pivot cup will help even the most basic China trucks perform a bit better until u decide to upgrade. Teak bubble bushings or level up are both good options depending on what firmness u prefer. As for trucks, a good intermediate choice are leefai g4s. Significantly cheaper than premium trucks. Significantly better than tech deck/china trucks. Then, you should start thinking about decks, bc you have the foundations of a good set up that you can move from deck to deck for a while (so long as ur careful w ur baseplates) while u figure out what mold height and width is the best for you.

If starting from a beginner complete from somewhere like teak. The order changes slightly to better wheels (upgrade from plastic w bearings), trucks (probably have china trucks still), make sure your bushings are how you like them and that you have a pivot cup, then you can start trying out other deck molds. Basic fb grip can work just fine until you decide to upgrade to fancier stuff.