If your goal is to improve as a photographer, a friend may not necessarily have the background to know what to look for -- often they'll just nod and say everything looks good.
Some websites can be brutal... some are a bit gentler.
But I'll offer a few tips on how to ask for critique. First... not everyone who posts photos on those sites actually wants critique. So check their guidelines, make sure you post on the appropriate section of the site, and then make sure you specifically mention that you're interested in critque.
Next... I do see people who post a huge number of photos. It's not practical for people to criique a huge number... so you usually wont get specific or useful feedback. I suggest you pick the best single image ... two tops. Pick an image that looks like you invested some effort to make it good (if it looks like a snapshot in which you invested no effort to take then people tend to ignore them.) Also... most people I know on those websites will not follow a link to offer critique and prefer to see the image inline on the site. Some will follow a link IF the link takes them to a well known photo-hosting site. If they've never heard of the site then they fear what may be waiting for them (or their computer) on the other side of that link.
Lastly... DO INCLUDE the EXIF data. When you're asking for help on your photography, it helps to include the information that lists camera settings (camera, lens, ISO/shutter/aperture, etc.) You may even want to add a few comments on what you were trying to accomplish and/or WHY you shot the image the way you did. This tells people you're actually serious and trying to work to improve.
The regulars on those sites see thousands of people come through... many of which don't invest the effort.