Read the map before you build: a habit that wins games
When a new tower defence map loads, most people start placing towers immediately. The players who consistently win do something different first: they trace the entire path with their eyes.
Where does the road curve? Where do enemies bunch up? Is there a spot that covers two lanes at once? Answering those questions before you spend anything means every tower you place has a reason.
I like to imagine the last wave, not the first. If I know a boss will crawl through the final stretch, I want heavy damage waiting there, and I build backward from that idea.
This sounds slow, but it takes fifteen seconds and saves whole restarts. Slowing down at the start is how you speed up over a whole campaign.
Try it on a map you've already beaten. You'll spot placements you never noticed while rushing.
