The very best practice is to a) send a blogger a pitch along w/ a license code. Also send us a video and some pre-made quotes. Your story needs to be easy to write (and ideally an actual story, but we'll take what we can get.) There are some items for which sending a license code does not make sense - for instance, enterprise software, security software, basically things we couldn't really use or evaluate. ("Another day, still no viruses, UI looks good. 5 stars.") If you think we can successfully use your product, send a license code, but err on the side of caution. A screencast might really can be very helpful for some personal productivity products, especially if it's something built to handle complexity.
b) give him/her some set small number of license codes to give away (5 or 10 if you're looking at something w/ a higher price point, more for something lower.) Free trials are really better here than license codes - something that turns off in a month would be just fine.
c) give him/her a discount code that they can send to their audience/followers and their followers/audience will get 20% off. This is actually a great alternative to giving people free licenses to give away, and in my experience works pretty well. And, of course, it will give you a much better idea of how your media outreach is working so you know who you should take out to dinner.