Over the past few years I've worked really, genuinely hard on creating a good writing portfolio. Although my efforts have waned in the last seven or eight months after finally getting a full time job that I love, it really was a priority for a while.
If you've read my post on going freelance and failing, you'll know that at one point I quit my job to go freelance, and it didn't go to plan. What was good about it however, was the amount of writing experience I got, and when I worked hard, how proud I was to secure it. Both before and after that I expanded my writing portfolio, and whilst it's by no means fab, here are some ways that I got started with it:
1.) Writing a blog. I always forget this counts. I have a lil secondary blog, which contains solely book reviews, so I always mention both if I'm applying for anything writing related.
2.) Getting involved at uni. I wrote a few articles for my uni paper and it was fab because 1.) They're online so you can provide links to them, and 2.) They printed them so I could take cutouts to my nan. There's also usually a writing society at universities, and they'll be all over any writing opportunities.
3.) Browsing sites like Upwork, People per Hour, Guru etc for work that suits you. The pay rate is usually pretty poor on all of these sadly, but I found that writing multiple articles most days helped me to really develop my own writing style, and find what worked best for me.
4.) Pinterest tips. The site's a bit of a minefield for this one - I found some absolute gems, but also some really unhelpful advice. However, it was the main resource that really helped me to get started with things.
5.) Contact local newspapers/magazines. This is very hit and miss, but I found a couple of really fab opportunities through getting involved with an indie magazine, and being accepted by them helped to boost my self-confidence massively.
I'm by no means any kind of expert on this, but I've loved expanding my writing portfolio into something I'm proud of. There have been so SO many big mistakes (like that time I got scammed of £500 worth of work - not a good day), tears, and upset, but I've also found a way of writing that suits me, and I'm so glad I have.