So just a pre-warning, a lot of my suggestions are more geared towards the hostel population, but some can be applied to hotel stays as well.

Stay at a Hostel

If you are traveling on your own, the best way to meet people in an easy setting is at a hostel. What better way to be pushed into interacting with people than to stay in a dorm room full of them? People of all ages stay at hostels and there is usually enough variation in characters that you will undoubtedly meet someone you can get along with.

Hang out in the common living areas

Whether in a hostel or a regular hotel, hanging out in the common areas is an easy way to interact with people while traveling alone. Hostel environments are a little easier to breech socially, as it is common practice to speak to strangers at hostels and even if you are shy, people will usually come up to you anyway. You may have to work a little harder at hotels and make the initial contact with strangers.

Make extra dinner – exclusive for hostels

An easy ice breaker with someone can be to make extra of what you are cooking for dinner and offer it to someone. At hostels, people are usually very open to free food as most are traveling on a budget. Make some pasta and sauce and share and I guarantee you will make a friend.

Hang out at the bar

Bars are known for drinking, talking shit and meeting people. If you are a solo traveler, head to the local bar even if it’s the hostel/hotel bar. This is the least intimidating place to start up a conversation with someone or even fall into another group’s conversation. Liquor makes people happy (mostly) and they will be more open to interacting with a stranger.
Join a Pub Crawl

Although not always available everywhere, pub crawls are the most fun way to meet people while traveling on your own. Pub Crawls are about joining a bunch of people playing drinking games before going out and continuing to drink at bars and pubs around town. Between the alcohol and the silly games, you are bound to make a friend.