Instructions
Buy at least one female monster. Female monsters have the female symbol, which looks like a stick figure with a line through the center. Look at the incubation time of each monster. The longer the incubation time, the longer it takes to make a monster.
Buy a male monster. Male monsters have the male symbol, which is a circle with an arrow coming off of it. Just like the female monsters, look at the incubation time.
Mate males with females that have a high star ranking. Star rankings show how good the monster is. Mating lower starred monsters together will not make a good monster.
Select monsters that are able to mate quickly. This increases their output.
Sell monsters that you no longer need. This gets you more money to buy food and medicine.
Continue breeding your male and female monsters until you have produced one with a five-star rating; this is the highest ranking a monster can achieve.