You don't. Avoid it.
These are the only things that can happen for you:
All these people and their family will dislike your photos and think they're shit.
They like the photos, but they will remember you as the guy who does photos for free and advertise your cost ($0) to everyone you've ever known. Now everyone else you try to charge will be mad and think they're getting ripped. They'll say, but you did it for them for free!
These people you shot for free will want photos again, for free. Because why would you be worth anything? You've already established your time and work is worthless.
Maybe you're thinking, if I charge them $0 they won't expect anything from me. It'll be easy!
WRONG. You'll get demands about editing, people demanding all your RAW files (because they dont want your shitty editing, doesnt matter if you think its good - they want the raws to use filters themselves. If you're really lucky they'll post their repulsive horrible raw edits on instagram and tag you). If you say No to anything, they will get mad and demand you delete all your photos of them, saying they dont give you permission for anything (after all since you're worthless you obviously had no contract or model release).
I could go on.
Do not ever offer to shoot for free. Practice, learn, get others (MODELS) to work with you for fun or in exchange for services. Worst thing you can do is go around town telling everyone 'I'm worthless, please let me take some photos.'