When I got started 10 years ago, there was nothing out there to teach me how to land writing work. Guru, Upwork, Freelancer.com, Thumbtack... all those bidding sites were pretty much it. (Don't know them? Good--stay away from them!) Basically, the problem was that I didn't know how to find writing clients, and the few prospects I had always wanted to see writing samples.
So I'd send my samples, and then... nothing. Silence. The only people I could get to follow up with me (and tell me "thanks but no thanks") were the people I knew in real life. I was a single mom and everything was riding on my ability to get writing clients. Talk about stress.
After years--and I mean YEARS--of struggling with the whole "relevant writing samples" thing, I finally figured out how to pitch clients and land work that paid real money, not just in "exposure" or maybe a couple of pennies per word.