Ok, so, you have first part down, give yourself chances to meet new people.
Next, it gets harder. Be nice, be interesting. Be funny, helpful, some combination of the above to give people you interact with positive memories/feelings for you. If you can swing it, be physically attractive. Do your makeup, wear nice clothes, etc. All this is just to get a good vibe.
Next you need time. Someone you have met three times who was nice and dresses well is an acquaintance. Someone you have been gaming/book grouping/camping with for the past 3 years who is nice and funny is a friend. Consistency is key.
Finally, if you have doubts, ask yourself the question: "would a friend act like this?" This goes for both you and them. If they call you up at 2AM because their car broke down, a friend would go help them.
If they invite you to do hard drugs on a work-night, they are not acting like friends, they are acting like addicts, and going out with them might be fun, but it will hurt you, and friends don't hurt their friends.
Friends don't always take and never give. So bring drinks to the meetup, but also don't be the only person that always brings the drinks. Etc etc, details depend on your circumstances.
I hope this helps someone.