The first obvious step is to actually be an expert in these specific topics.
This measn that you do have the skills, knowledge and answers people are looking for.
The next step is to communicate in an effective way.
If you don't speak out and position yourself as an expert, your potential audience will never know you even exist!
This means having a website, platform or blog which works!
You then need to have enough exposure for your site.
Media coverage gives you that type of respect.
Confidence and attitude will give you the edge as well.
Make this simple experiment:
Take an expert's site or blog and ask yourself: why do they get credibility from you?
There are always good reasons!!!
then check your own pages and material and ask yourself: "would I give myself credibilty if I was seeing this page?" Yes? No? Why?
In most cases you will get a very clear answer in no time on why you have credibility or not.
Next, trust your instinct and take action to reorient whatever is not on track!!!