The first thing is try to concentrate your pairing based on weather, pay attention to low pressure, pair if it rains, if it's snows it's even better.
A lot of the other tricks will be difficult if you only have 2 animals, what breeders or pet owners do is use other animals to their advantage. They use sperm plugs and shed from another male, leaving the shed in the female's enclosure and smearing the plug on the female's black. They also use shed and bedding of other females. Finally they also do 1.2 pairing it sometimes helps.