You've got to look at HARO as more than a backlink opportunity service as it can offer so much more - if you get it right. You need to make sure that your pitch for each and every request is on point, otherwise, your pitch will just get ignored.
As a basic, make sure you have a decent and professional photo (usually a headshot) as well as a Linkedin account that also looks professional. The reason? When they (the reporters or people requesting submissions) they will ask for you to state your credentials - why you're an 'authority' in your field or the topic to be reported on. You may be asked for social media links too, so make sure these are on point too.
Check your spelling and grammar in the pitch too - if you're pitching to Forbes or other, more high end, media outlets then your text/pitch needs to read well. Don't oversell yourself - they usually have lots of pitches to read so make sure you are to the point and concise - ie read what they have requested.
You are also going to have competition from the premium HARP members - they often get the emails way in advance, so don't be disheartened that you get no reply. Often the same people are requesting a pitch/story, so you can be sure they will ignore your message if you spam them!
Get ti right and you not only have a backlink but you may build a relationship with a reporter or other editor etc that can give you further, direct requests in the future. Or, at least, they will be more likely to consider your pitch as it has been well received previously.
Get it right from the start. Don't be disheartened or lose faith when not responded to. Remain professional. Don't spam.
Also, and finally, don't forget that if you create a longer pitch (if requested) then you have the basis for an article or news story for your own site if not used or selected
