Norton Sterret, in How to Understand Your Bible, states very concisely some of the major principles that need to be adhered to when building a theological system from ones own study of the Bible:
1. Base doctrine on the literal statements of the Bible rather than on the figurative portions.
2. Base doctrine on plain statements rather than on obscure ones.
3. Base doctrine on the didactic (teaching) passages rather than on the historical ones.
4. Base doctrine on all the relevant passages, not on just a few.
5. Do a word study to learn some doctrines.
6. There are doctrines which have no one word in the Bible to describe them.
7. There are passages in which a doctrine is presented but the actual word does not occur.
8. Some doctrines have more than one word to express them.
9. Be sure that each passage is understood through the general principles of interpretation.
10. Be cautious in formulating doctrine by inference.
11. Beware of doctrinal speculation.
12. In forming, holding, and teaching doctrine, emphasize what the Scripture emphasizes.
13. Seek the practical import of the doctrine.