With breeding it goes like this
Same species and different ID number
"The two seem to get along very well"
69.87% chance of getting an egg every 255 steps
Same species, same ID number
"The two seem to get along"
49.5% chance every 255 steps
Different species same ID number
"The two don't seem to like each other"
19.81% chance of an egg every 255 steps.
Different species different ID number
"The two seem to get along"
49.5% chance ever 255 steps
Different egg group, same gender, or undiscovered egg group
"The two prefer to play with other Pokemon"
0% chance to get an egg
These are the only things that influence breeding. Also everybody can breed with Ditto unless they are legendary or baby Pokemon.