As a fairly optimistic and happy person, it's not hard for me to maintain that. I do have my moments, though, when I have to make an effort to get back to my "happy place." These moments usually happen at work--home is my sanctuary, and it's a rarity that I don't feel contentment here. Home IS my happy place.
When I do need to consciously make an effort to stay upbeat, I basically just think about how grim and "unfun" my current state of mind happens to be. I think about how it's much more enjoyable when we're all laughing and joking. One of my favorite things to do is to laugh, or to make other people laugh, and it's hard to do that when you're in a snit. There will always be a certain amount of negativity that you're exposed to, but I try not to let myself get bogged down in that. If it gets particularly bad, I have the ability to tune it out. If I'm especially focused on the task at hand, people have joked that I'm in my own little world, and they'll have to work to get my attention. (I think most of my coworkers understand by now--after almost 10 years--that sometimes I really do get very focused, and I hope that they don't take offense.)
When it comes to remaining upbeat, I try to remember that in the large scheme of things, I've got a good life. It's not that I think that I've got it so much better than others, but I believe it's appropriate to feel thankful for what we have, and I have much to be thankful for. The most important thing I'm grateful for is the wonderful people I have in my life, whether it's my husband, my parents, my family, or my friends. If I wanted to be negative with such positive influences in my life, I'd have to work very hard at it!
I've had discussions with my Mom about seeking out the positive. It can be so easy to get overwhelmed by the bad things that happen in the world, whether personally, locally, or globally. We show our humanity by grieving for such things, we show our nobility by believing that there can be a better world, and we show our compassion by doing what we can to help achieve that. While we may not be able to fix a broken world, we can sometimes fix a tiny little part of it. And millions of tiny parts add up to the whole.
Nothing is achieved without hope--and optimism.