How to Improve Your Karma
Karma, the law of cause and effect is produced by our actions. A cause is like throwing a stone in a pond.
The ripples that radiate out are the effect. You, standing on the shore, receive the results of this action. This is karma.
Good actions which benefit ourselves as well as others give rise to happiness. Continual good actions accumulate positive potential so that good things happen to you in turn.
Bad actions which harm yourself or others give rise to suffering. Bad actions store up negative potential so that bad things happen to you in turn.
If bad things happen to you but you think you've been a good person, it could be bad karma carried over from a previous lifetime.
You can shift this by doing good deeds like charity work, making offerings at your place of worship, asking for intercession prayers from your spiritual leader and doing purification (making a pilgrimage to a holy place, doing a retreat, fasting, making confession). Selfless acts or sacrificing, like giving your whole lunch to a homeless person, is a stronger good action than,say,giving them just an apple from your bag.
If nothing is moving in your life, it's an indication of neutral or stagnant karma. Good things will start happening in your life if you start doing good actions towards others. You've just got to get the momentum going.