ONE WAY to change your perspective is to change what you're comparing your situation to. This is probably one of the easiest ways to change your mood quickly. For example, if you're feeling kind of grumbly about having to get up and go to work in the morning, if you gave it even ten seconds thought, you could find many things to compare it to that are much worse. You're not in prison. You're not in a concentration camp. You have enough to eat. You aren't worried about a tribe coming and chopping your arm off with a machete, etc.
You are already comparing your situation to something. Naturally and automatically, we usually compare our situation to something better. Although that's natural and automatic, we certainly aren't stuck with it. A little deliberate comparison can go a long way.
Think of something you are unhappy about. Now notice that the reason it makes you unhappy is that you are comparing it to something better. You're comparing your situation to something more ideal. But try this: Think of someone in this world who would take your situation over theirs in a heartbeat.
Whatever you are unhappy about, you can easily find a worse situation to compare it to. And from that perspective, you are lucky to have the problem you have, even though it is obviously not ideal. Who says the ideal is a legitimate thing to use as a comparison anyway? Something worse is at least as legitimate, and has a benefit too: You feel better.
This is how to feel grateful for what you have. Once you know how, it's very easy and works every time. Read more about this here: Comparison.