Mammillaria surculosa

Keep them cool and dry in the winter.
In summer give them a good soaking every time the soil dries out.
Also give them a feed of tomato liquid about twice during the spring and summer.
Keep them in a light place, where they get direct sun for part of the day, but on a very hot summer's afternoon they may need a bit of shade.
Small cacti will need fresh compost every 2 or 3 yrs.
Mammillarias usually flower easily :)
Good luck ! I will look forward to seeing their photos next year :o)

Great tips Hywel!

My small mammilaria didn't flower this year. I'll try to follow your instructions :-)