The best way to come up with thesis ideas is to combine personal interest in a topic with relevant research and guidance from a teacher or academic adviser. One of the reasons that it is so important to incorporate personal interest is that a thesis, whether it is for a master's or doctorate program, will require quite a bit of time and effort. This time and these efforts can seem quite daunting if the research topics that will inform the thesis are of little interest to the student writing a thesis. It is also important to work with a trusted teacher or academic mentor when coming up with thesis ideas. This person can help one to develop thesis ideas into thesis statements and can also offer guidance in terms of research methods.
In many cases, the germs for thesis ideas will come from coursework and independent research that the student conducts as part of class assignments. A graduate student may develop thesis ideas based on lectures that she attended, books that she read as part of required reading for her classes, and research that she conducted on her own in order to complete assigned projects. All of this work will inform the student's knowledge regarding the subject that she is studying. Hopefully this work will spark particular interest regarding ideas or theories that are discovered as part of the learning process.
When coming up with thesis ideas, it is useful to think back on all of the coursework that has already been completed and ask oneself if there was a certain topic or theme that one wanted to know more about. A graduate student in an English program, for example, might think back on some coursework that she completed on Willa Cather and the pastoral novel. Considering this, she might come up with a list of thesis ideas about Willa Cather and the tradition of the pastoral novels and then review these ideas with a professor or thesis adviser.
Once a subject has been chosen for a thesis, it is important to consider the various ways in which that subject can be investigated. The graduate student might think about comparing and contrasting Willa Cather's pastoral novels with her novels that take place in urban areas. Or she might consider investigating Willa Cather's novels as feminist texts. It is best to consider a number of angles before jumping in to the research process.