The first three waves decide everything in tower defence

After hundreds of tower defence runs across different games, I've become convinced that your opening is the whole ballgame. The first three waves look harmless, and that's exactly the trap. They're your only window to build economy without stress.

My rule is to never overspend on damage early. A cheap tower that slows or weakens enemies buys you time to set up the expensive stuff. Panic-building a powerful turret on wave one usually leaves you broke for the wave that actually matters.

Position before power. A mediocre tower at a perfect chokepoint outperforms a great tower in a weak spot every single time. Learn the map's corners and long stretches, and plan your lane coverage before you spend a coin.

When a game gives you a scouting option to preview upcoming enemies, use it obsessively. Knowing whether wave four is armored or fast changes which upgrade path you commit to.

Do these things and the mid-game stops feeling like a scramble. You'll be reacting from a position of strength instead of plugging leaks.