Border geraniums or pelargoniums?
Pelargoniums need a really sandy/gritty soil, and develop a hard callous before roots start to develop, which can take 4-6 weeks in the warm.
Cuttings need to be about 4ins long and remove most of the leaves before potting them. Keep them barely damp as they will rot off easily, so don't cover them with polythene. They need to be somewhere warm, but not in strong sunshine either.
Border geraniums are easiest if you lift the whole plant and pull it apart into smaller portions, each with its own roots.
Not really relevant, but when I put some old pelargonium plants into slightly bigger pots this week, I found 5 seedlings growing in the pot, they had self seeded, thanks to me being a lazy gardener and not dead-heading them.
Needless to say they now have their own pots