The best option would be by air. There are daily flights to Gaborone from Jan Smuts Airport, South Africa and also from Harare, Zimbabwe.
If you're in South Africa, Zambia or Zimbabwe, Rail might be a reasonable option.
Finally, you might come by road. I strongly recommend that if you choose this option, you make sure that you can get to atleast the bus terminal, if not straight to University of Botswana. If you need to be picked up from the border, it had better be the Tlokweng gate- otherwise you'll be faced with a rather challenging mini-tour all of your own.
If you can manage to get to the airport (Sir Seretse Khama), the train station or the bus depot, let us know when you'll arrive and we'll be there to meet you. The same applies to the Tlokweng gate.