Usually Buddhist prefer to use the word 'rebirth' instead of reincarnation.
According to the scriptures, in order to be reborn a human, we have to have the basics of the Five Precepts: to undertake the training not to harm living beings; to undertake the training to abstain from stealing; to undertake the training to abstain from sexual misconduct; to undertake the training to abstain from false speech, and to undertake the training to avoid intoxicants which confuse the mind.
So, according to the scriptures, if we want to be reborn human, we have to undertake those five trainings to avoid unskillful actions in our virtue. This is because the results could be that we go to another realm, down. The animal world usually has much more suffering than for humans, and therefore we have to be careful about our virtue. In order to be reborn human, keeping a level of virtue that is harmless is a requisite.
Also, transforming and making a lot of good Kamma to balance any negative Kamma we have done when we were unskillful in our past, is necessary so that the power of that good Kamma raises us up. In that sense, we look at a half filled cup of hot water and dump half a cup of salt in it, and stir it up. The half cup of salt is our bad Kamma: unskillful actions. We stir it up, do we want to drink it? "No, very salty! Yuk!" But, if we pour it into a bathtub, add lots of buckets and buckets of clear fresh water, it dilutes it, dilutes it, dilutes it, dilutes it. The more we practice properly, the more we're doing skillful Kamma, this helps to dilute any past negative Kamma performed due to not being ignorant of the results.
When we build the power of virtue, generosity and walk the Noble Eightfold Path, we are making very skillful Kamma which, according to the teachings, will enable us to be reborn a human.