Just be yourself: unless you are normally taciturn and unapproachable. Be prepared to talk to others and, just as importantly, listen. Be genuinely curious about other lives and be prepared to answer the same questions you'd like answered. I've had really good experiences that have lasted for as long as it takes to drink a cup of coffee or for life in an exceptional case. It's easier when you are young.
I have never found it a problem, and I am an introvert. Most everywhere I have gone -- which includes most of Europe, Canada, Mexico, and Down Under not to mention most of the states here in the U.S. including Alaska and Hawaii -- if you are showing interest or asking questions about anything, most of the local people are delighted to talk about their community, landmarks, history.
Staying in hostels is good. I’ve only stayed in a few and you don’t always make friends but people are generally friendly and there’s usually other solo travellers.
Use my “once-a-week” rule: Be sure to bathe, change your socks, and rotate your underwear from inside to out and from front facing to back, at least once a week. This allows you to travel light, and keep the B.O. to an acceptable level 👻
My wife and I travel in our motorhome. I usually talk to the the office and I also walk the campground. More for exercise than than anything else. I say hello to everyone. I'll talk to anyone open for a conversation. I try asking everyone a question even if it's just where is a good place to eat. After they give you an answer tell them you are new in town and ask if they care to join you. I also try giving everyone a compliment. This usually works for me.
Having a few card tricks handy. Absolutely brilliant ice breaker. You can go up to almost anyone, show them a good card trick, and they’ll want to be your best mate. 😊😊😊