Understanding the Snake
The enemy is a long segmented snake. Each segment has individual HP displayed on it. Your towers damage whichever segments are in range as the snake slithers past. Damage only the tail segments and the head keeps moving forward.
Optimal Tower Placement
Place towers at curves where the snake passes close to multiple slots. This maximizes the number of segments in range simultaneously. Chokepoints where the path narrows are especially valuable.
Upgrade Priority
Early on, spread towers across the path rather than upgrading one heavily. Once you have basic coverage, invest in damage upgrades for towers at the tightest curves.
Managing Resources
Each defeated segment drops coins. Save for tier-2 upgrades rather than spending on small improvements. The damage jump at tier-2 is significant enough to change your defensive capability.