Everybody suffers rejection at some time or another in their life. The first step in handling rejection is to recognise that rejection is a necessary part of our private and professional lives. No success is achievable without encountering rejection of some form along the way. It encourages us to hone our skills.
Let me use an example. Imagine that you are the author of a novel. In order to get your novel published you are going to have to send a manuscript to as many publishers as possible. Unless you get lucky, you are likely to have a very high rejection rate. However, this should not be viewed as failure, but merely as a part of the natural process of success. Every road to success includes backward steps as well as forward.
Publishing is famous for the high rates of rejection that new authors encounter. If the publishers you have been in contact with are complimentary about your work, then you should take heart. However, if there is something at fault, it needs to be changed. Then you can send in your work again. This process of re-working your manuscript will bring it to the point where you can be sure it is your best work. Your best work would not have happened without the rejection.
Which brings us to step two. Step two is simply to acknowledge the above i.e. that you are going to encounter rejection, no matter how good you are, and change your mindset to embrace this. I am not talking about trying to kid yourself, but if, after careful consideration, you are happy that all is well, then you should feel confident that the end result you desire will come to fruition. In this particular example, that is getting your book published.
Go into every fresh challenge with the knowledge that each challenge is taking you one step closer to your goal. In achieving your goal you are going to take backward steps, so enjoy them, too, knowing that they are in effect moving you forward. If you never got rejected, you would not get better at what you do. Rejection is necessary for progress. This is the mindset you need when you are handling rejection.