"Charge them that are rich in this world, that they be not highminded, nor trust in uncertain riches, but in the living God, who giveth us richly all things to enjoy." 1 Timothy 6:17
The key here is that God gives to all liberally and God has designed us to enjoy life. There are many ways that you could advance your joy meter. Be friendly to other people. You might find out that not everyone is like those who have misused you or mistreated you.
Take a walk every day (if you can) and just enjoy the natural beauty surrounding you. That's what it was made for.
Sit back in total silence and let God speak to you. There is no enjoyment quite like hearing the voice of God. (Wait, don't say you can't hear the voice of God. You might have to get away from all the other voices around you for a moment, like; TV, radio, your spouse, the Internet, your ipod or blackberry, but you can hear the voice of God)
Create a hobby or re-start where you left off in that hobby you really enjoyed. Even if time has gotten in the way and years have passed, most of the time you can pick up where you left off. If not, it's time to begin anew.
Give something to someone. That's right, just start giving things away (and I don't mean ripped up and torn things or old junk that barely works; that's not giving) give something of value to someone; maybe a grandson or granddaughter, maybe give something to someone you have never met. Last week I met a young black man at the grocery store. He is a business major at the local college. I sensed that he was a reading young man and he is. I brought him three of my favorite books 2 hardbacks and one soft cover, all in great shape. These were books I had been planning to keep in my collection, but God was tugging on my heart and I gave them away.
Plan a scheduled event for yourself. Do something you really want to do for yourself. I know money is tight, but you can't always use that as an excuse. Maybe you will have to work hard, plan and save, but to just keep making excuses why you can't do it is not good for your soul. Maybe you have worked all your life and you are on a fixed income and it just looks impossible. Maybe it is impossible, but with God all things are possible. Pray about it and see the mighty hand of God minister to your personal needs and desires. Of course God wants you to be happy and enjoy life. Who has been telling you differently? They are mistaken. It is not selfish to do something for yourself.
It amazes me at how mixed up Christians are today. I blame the watered down preaching coming from men and women who haven't seen the fun-side of God. So many preachers have been taught by stiff-necked, callous, letter of the law professors that they haven't taken time to build a relationship with God and get to know more of God's perfection, which includes: laughter, joy, peace, enjoyment, fulfillment, enlightenment, happiness, pleasure and fulfillment of desire.
God richly gave us all things to enjoy. Let's get on with it.