To be solid and valuable, your hypothesis should be able to pass the "So What?" test -- meaning that it is relevant and important, not trivial. While some topics may only garner interest from limited quarters, your hypothesis should still be valuable to someone, whether it be the world at large or players within your specific academic discipline. Additionally, the less important your hypothesis is, the more difficult it may be to do research on it; if the topic lacks meaning, there may be limited resources available on the subject. Setting long-term goals for your hypothesis can help you ensure that your subject matter is relevant and meaningful.
A solid research hypothesis is neither too narrow nor too general. Create a too-general hypothesis and your hypothesis will quickly degrade into the obvious. Develop a too-narrow hypothesis and you will find yourself lacking in sufficient material to prove your claims. While specificity will vary between disciplines, consulting with your professor can help you choose how to best narrow or broaden your hypothesis to make it solid and viable. Similarly, it is important that your research is narrowly tailored to your hypothesis; irrelevant information can bog down and distract from your true hypothesis.
Your hypothesis should be observable and measurable, so that it can be definitively proved in your project. Information that cannot be proved is not helpful; hypothesis statements are not opinion, they are fact, and you must be able to prove them with original and secondary research materials.
A solid research hypothesis must be well-organized and simple. While the research backing up your hypothesis may potentially be complicated, your hypothesis statement should not be. In addition, your hypothesis statement should be brief and to-the-point; don't attempt to prove your entire hypothesis and flaunt all your research in your hypothesis statement.