1) Know your voice and its limits
Every voice has certain qualities that fit to certain songs and styles, match that with your personal taste and that is a good way to begin. You can always learn different techniques but there will always be certain songs that idiomatically fit your voice and there are some that do not
2) You do not have to use your limits every time you sing
Every songs does not require a riff/run. There are some songs that require simplicity. Singing the gospel is not to draw attention to how well we sing but to edify the God who granted us this talent. Every song does not have a 2.5 octave span. I always suggest learn any new song without a single run and then begin to finagle the melody. In addition, it is not very smart and will tear and wear your voice out very quickly if you are not careful (Shirley Ceasar)
3) Rest your voice and warm-it-up religiously
It is never a good idea to sing without being warmed up. It is the same rule athletes follow before every single game. The vocal tract is a series of muscles, organs, and ligaments that need to be warmed-up just like athletes. It is also of the utmost importance to rest your voice equally as well. If you know you have to sing a revival 4 nights in a row, rest your voice about 4 hours before and warm-up about an hour before as well (warm-up do not have to be hard and take a long time, just efficient). This process also includes drinking WATER throughout the day. Drinking water only around the time you sing will only handle immediate surface level dryness. In order for your voice and body to have the water into your blood system you will need to be drinking AT LEAST about 3 hours before).
4) Oversinging and growling all the time does not equal singing soulfully (this is in general for every genre)
I cannot stand this about gospel music which is why I have to defend it in pedagogy courses where they assume that it is all unhealthy to sing. NOT TRUE. You can sing any genre of music unhealthily. Learning a strong foundation in support and as much relaxation of the throat will carry you a long way in preserving your voice (especially if you want to be a professional)
There are so many more intricacies to each of these "Rules-of Thumb" but this just serves as an introduction. Again, I reiterate that these are general guidelines and NOT law.
Any questions regarding specifics, clarification, pedagogy or anything for that matter. Feel free to ask. I am currently working on my M.M. in Vocal Performance and hold a B.M. in Music Education.