I don't really think there are any specific guidelines to making friends, but you have to go out and find people and talk to them in order to get friends.
I agree with clubs and interest groups. Classes, be they educational or hobbies, gym classes too. I had a friend who joined a bike club and met a bunch of people there, they went mountain biking each weekend and snowshoeing in the winter. For me, I wouldn't say a bar or nightclub. I would rather meet sober people and then share a drink when we get to know each other. As for online, well, forums like this is good. I only joined last week and I already feel like I have some nice friends I met here online!
Volunteer for a company that does group Volunteering (So you meet people rather then work alone) and do it often for a while. You'll make friends in no time Do something outdoors too like Gardening as it means you will get fresh air