A good template is drawn once and sold dozens of times. A bad one is drawn once and sold once.
Keep the slot generic
The blank figure should suit as many body types and species as possible. Every distinctive detail you add narrows your buyer pool.
Crop deliberately
Half-body templates sell faster and cost less to fill. Full-body templates earn more per sale but take longer.
Leave room for hair and tails
The single most common reason a template cannot be filled is that there is nowhere for long hair, wings or a tail to go.