I have found that when I have tried to sing outside my range I have developed problems.
i) warm up your voice before singing
ii) learn what your range is and only expand this gradually
iii) if you start singing more then scale down your other vocal use, e.g. talking in bars, shouting.
This is a link to my experiences of vocal injuries
Look after you voice when you speak;
i) minimise shouting and stressful arguing
ii) When speaking always use your normal voice e.g. by speaking at a normal volume. This is something that probably applies mainly to people who are prone to anxiety like myself who sometimes change their voice according to who they are speaking to because of anxiety when speaking to certain people in certain situations. Changing this anxious way of speaking by speaking in a normal way at a normal volume is an example of changing the way you feel by changing the way you behave. Speaking in a normal voice can reduce anxiety in certain situations and is probably best done when you change the way you think about those people and situations.
Resting your voice
If you want to rest your voice then apply the idea of recovery time and you will find that there there are plenty of opportunities when talking with someone to take a break from speaking by listening because in general people prefer to speak than listen. I’ve noticed that when I do listen more to other people they tend to listen more to me. This is particularly important when in noisy situations where you are having to strain to speak. It also carries the added benefit that you can learn more things from other people.
Vary how you use your voice
Avoid speaking in a monotone and try to ensure that you have natural variation in tone in your voice when speaking.
I think that I may have got a hernia through doing blow bends on my harmonica. So possibly avoid blow bends and anything that involves using a lot of force.