I have spent a good part of the last 6 - 7 years helping run and manage one of the more popular reseller membership sites (since I am so new here, I will not mention which one).
One thing I couldn't agree more with is the "YOU NEED TO BE DIFFERENT" factor that has been mentioned by EVERYONE who has responded to your question.
I can not emphasize this enough. Simply downloading a product, and uploading it AS IS, to your own site, will not cut it, especially if you're just starting out.
Since you asked about PLR products specifically, you SHOULD do all of the following:
1. Rename the Product
Examine the contents of the product and think of a better name.
2. New Images
Create higher grade, more professional looking images. Outsource this part if you have to, but to make your product different and SUCCESSFUL, you need to make it stand out from the crowd.
3. Add More Elements
If it's an ebook, record yourself reading it and add the audio version. Create text based "slides" and record it as a video (showing corresponding slides as you read it). Create a new sales page affiliate page, thank you page, lead page, etc. to really make your version different and stand out more...
4. Sell it for a FAIR price.
Lose the whole "$7" or "$17" mentality. Price YOUR new product according to how much time and effort you put into it. Price it based on how popular the topic is and how wide or targetted the audience is and definitely base the pricing on how much REAL CONTENT is within the product. If you TRULY do have the answer to "How to Make $1,000,000,000,000,000,000,000,000,000 In Your Jammies While Laying in Bed", don't be stupid and sell it for $2.99. People are NOT stupid. People do not mind paying a real world price as long as they are receiving a real world value.
No matter what you do, the bottom line is that in order to be successful with PLR products, you really do need to make it different.
Also, another way to be successful is to NOT try to promote to just the IM industry, that's when you'll really get stuck. Everyone in the IM industry is already promoting to everyone else in the IM industry.
If you purchase an ebook (with PLR) about domain flipping, for example, once you've changed it, added to it, whatever... visit and promote YOUR ebook to the tons of domain registration companies' forum members. If you buy an ebook about fishing, once you've made it your own, find a slew of fishing related forum sites and promote the hell out of it to those members.
(NOTE: It's important to note that you should only perform the above IF/WHEN you know enough about the subject matter. People want to buy from people who KNOW what they are talking about. If you don't, they will see right through your sales efforts.)
Sorry this post got rather long, but this particular subject is one I am passionate about. So passionate that I have created many sites and mailing lists related to this exact topic. You can't just buy a product with resale rights and make a killing reselling it. It just ain't that easy anymore. You really have to make YOUR copy stand out.
If you, or anyone else, wants more useful tips, please feel free to PM me. As I said, I am very passionate about this exact subject and love helping others succeed in the "im/reseller" industry.