Develop more confidence in yourself. Often people worry a lot about the future, because they project a limited idea of themselves into the future and believe that they lack the capacity to deal with whatever may arise for them. Or people may worry because they are afraid of Dukkha. They want to figure everything out so they can only have pleasure and avoid Dukkha. If we are able to grow in the acceptance that Dukkha does exist, then we won't worry as much. As well, if we can have more confidence in ourselves then we may believe that we can deal with whatever comes.
If you develop more confidence in the Law of Kamma, do more good Kamma, and reflect on it, you will worry less. This is because you will not be so concerned about the results of your actions or unbeneficial results coming to you.
Some people may bring up the doubt, "But what about some of the bad Kamma that I have done in the past?"
Firstly the Buddha encouraged us to reflect on our good Kamma not our negative Kamma. By reflecting our good Kamma, we can develop more confidence in our ability to practice, and use any Dukkha that arises for us as an opportunity to develop the Paramis.
So if you develop more of a positive outlook on Dukkha, that Dukkha is an opportunity rather than a calamity, we can learn how to worry less about this and take one difficult situation at a time.
Also people worry a lot because they feel they have to figure out everything in advance. However we may never even go in the ways we imagine we will, so we don't have to figure out everything right down to the last detail.
Often we go in completely different directions that we thought we'd go and sometimes situations arise we don't even expect.
If we reflect more on death, how the future is unknown, and try to open to whatever arises for us, whether it be pleasant or unpleasant, it will also helps us take advantage of the possibilities and the opportunities that arise for us, rather than thinking we have to work out our life down to the last detail.
A healthy sense of confidence, self worth helps in not projecting a limited idea of our abilities into the future. For example, perhaps you are having a difficult time sleeping, which some people do from time to time. Often the worry is worse than the actuality of the next day when we are sleepy or tired. So rather than getting worried that we won't be able to deal with it the next day, due to lack of sleep, we can try to remember a time when we didn't get sleep yet it was fine the next day, and we dealt with it quite well.