Travelling around Kowloon you will find yourself again using the road as the main artery going north-south through the district.
As the Mass Transit Railway (MTR), the underground railway system, has a main line following the road it is most often easiest to use the trains when moving from one section to another.
Consider taking a walking tour of Nathan Road starting at the southernmost tip and walking as far as your interest or fortitude takes you through the various different types of districts. And when you have had enough, take the train back to your starting point.
Alternatively, you may try the Blue Route of the Big Bus Tours which is the hop-on hop-off bus you see in London and Rome to tour around the Mong Kok, Yau Ma Tei, Jordon and Tsim Sha Tsui of Kowloon. It gives you some ideas of what the major sites of interest like when later on you can visit that again on your own.