Depends on your niche and your level of expertise.
In some niches, you can search for the industry standard. Then decide if it sounds about right, too little or too much for you.
If you’re just starting, don’t have much experience, or no recognizable training in it, then you’ll probably have to start on the low side.
If you have a track record and an advanced degree, then you can go for higher rates.
Ultimately, you’ll find out when a serious prospect starts to negotiate with you.