Well it is my thing and I thought I would share with you, because after several years of nesting grass snakes I have a few observations and really simple tips which may help these beautiful creatures.
First how do I know they are successful? Each year when I take the compost material barrow by barrow to the kitchen garden I find their old eggs. Each with a perfect slit at the top like a turtle egg so you know they have hatched and that in itself proves the compost temperature is working as it should. Twice I have found some of the newly hatched in late August, once in the pond and secondly under a pile of leaves
The old eggs are always at the bottom sort of glued to old leaves so the snakes are laying on a base of old leaves and the first cut of grasses I continue to heap on as the season progresses. That juncture of leaves and composting grass must be to their liking. Also, the two compost heaps are made from a square of stood up old wooden pallets and the nests are close to the open slats so air and access is also important. I would say its important not to use a solid structure or at least make some holes at the bottom.
The location is probably a factor with the compost sheltered and facing sun towards the sun. Around the area I have left grass to grow long with only a neat path mown and all the long grass I leave apart from a cut in October. This includes a nettle patch next to the compost where I sometimes find snakes sunbathing - presume this is them staying close and guarding the eggs. The rest of the garden is full of wildflower areas and plenty of undisturbed corners.
Simplest advice is leave well alone as much as possible although they obviously don’t mind the mower sound each week, but I think not turning the compost is the most important factor or making it too tidy. This includes not strimming, at least until October while the adult and juvenile snakes are still active. I think strimmers should carry a wildlife warning.