1. Create and optimise your own site
And it can become part of your portfolio! There is no place better to run SEO experiments and try out tactics and strategies that may be too risky for a client. You also don't need to anonymise the data on your own site and can completely transparent with your own site's SEO campaign.
2. Do a few projects for free for friends/family
Again this is a nice entry way into dealing with another brand. If any relatives have a website which is fairly low performing already - you can put together a free SEO campaign for them when you have time.
3. Take SEO courses
I'd take multiple SEO courses one after the other so you can be influenced by different ideas and principles - read articles about Technical SEO, Link Building and Content Strategy.
4. Follow and learn from established professionals
Most of what you will learn comes from quietly watching how other experienced SEOs think. Go on linkedin and find SEOs with large amounts of followers who maybe live locally.
5. Join freelance SEO platforms
These platforms are not glamorous and the pay is not amazing at first, but they're a good way to build a reputation and can lead to larger SEO clients. PeoplePerHour is my platform of choice.
6. Build a social media presence
You do not need to be loud or viral, just consistently share how you think about SEO. Share screenshots of your work (and make sure you get permission from any clients before doing so).
7. Network and collaborate with digital marketing professionals (especially Google Ads/PPC experts)
DM Google Ads and PPC specialists in the local area to chat about how their freelance career is going - you never know where it might lead!