Without actually seeing your site i can only make a few suggestions here...
Firstly what is the navigation like on your site, is it easy to find stuff quickly or do visitors need a degree to work it out.
Do you have annoying popups that keep appearing?
Hard selling straight off can put people off, better to build authority and trust and recommend stuff rather than in your face selling.
Are your posts written using lots of fancy words and tech jargon, people who find your site might be new to the subject so a softer approach might be better.
Are you saying something in 1,000 words when 400 would do, long winded blocks of text is off putting.
Are you using videos or images in your posts, helps to keep people longer when they can watch stuff
do some keyword research and give your visitors what they want.
Add a news feed for your niche, can help keep people longer
I hope this can help a bit