I agree with a lot of what has been said, but finding that person is mostly luck. But you can increase your chances by doing a few simple things:
1. Make yourself available. Sitting at home is the worst thing you can do. On-line dating is better than nothing, but pales in comparison to being out in the real world, meeting real people with few pretenses.
2. Show that you care about yourself, by making an effort with your appearance. BE CLEAN.
3. Be sociable, but leave desperation far away. Keep an eye out, but don't hunt like you're just dying to find someone.
Yes you won't have any luck catching fish if you don't actually go fishing. Also all that practice is going to help you when you do meet someone who likes you.
Really I think if you're lonely and not so young that you think you have plenty of time you need to work on meeting people especially if you're not in a super social job. If you're feeling the pressure of being alone, press back. A lot of people do not do this. They usually have lots of reasons why they don't get out there and try, none of which make a lick of sense.
Reasons I've personally heard:
They have some ideal whether romantic or spiritual that means the universe or jesus or karma is going to take care of them and bring that person right to their doorstep. Going out and searching would mean you don't have faith in the wonderfulness of whoever you think is looking out for you. These people talk a lot about patience and faith and real love being worth waiting for.
They are focused on not wanting to get hurt. They have been hurt before (usually this means they asked someone out and the person said "no") and they are not ready to risk that again. Sometimes they present this as being because they are just sooooo sensitive. Okay well for fucks sake you are not made of glass, get over it this is a human experience and not something that makes you too special to try. I'm not talking about people who had terrible things happen in serious relationships, I'm talking about people who talk like this about rejections and not being the hot looking one girls/guys like.
Feeling trapped by their current life circumstances. It's always a better job or living situation or losing weight or the dependance of their kids, parents, loser siblings.. whoever, SOMEONE who depends on them and so they really can't fit a relationship into their life until some huge long list of circumstances changes, but they are still lonely. I had an older friend who when I met her was like this about her young adult kids and is now like this about her grandkids so basically she'll never be in a place she considers spacious enough to include someone else even though she is desperately lonely.
Here's a fact: if you have been alone for a long time and relationships seem very hard then working on getting a relationship is going to mean getting out of your comfort zone. Even if we feel like our life is fucked in some way it is still our comfort zone because it seems that much harder to do something about it than to continue on in it. A lot of it is habit, you become comfortable with what life serves up to you without any effort on your part to obtain it. Doing something radically different is going to affect your comfort zone and it's incredible how possessive people are of that comfort zone, how they freak out that it might get altered in some way. But that's what an active, growing, dynamic life does, it alters. It's pretty hard if you've passively allowed life to happen around you for years to see that there are other ways of being, especially since those ways are going to have costs and risks.
I've had RL friends now who have spent over 20 years in these situations, all the time never making any direct moves to meeting someone. It's frustrating and sad. That is why I am lecturing you all now