Here are the steps to follow in order to perform well in codeforces contests:

1- Have a fast internet connection: codeforces servers might be heavily loaded and be down, but during the down period the server might be up for short moments, and if you have fast connection you can catch theses moments and get chance to open the problems or submit your solution, also when you finsh coding a solution in the last minute you need fast connection to quickly submit

2- read all the old problems on codeforces: admins nowadays allow problems to be repeated or to be very similar to some old problem (or at least they don't take care to avoid that), so if you read all problems on codeforces (you don't have to solve them) you can know that a problem is repeated and copy/paste one of the solutions of the old problem, you might take some time to find the old problem but it can still be less time than to solve it.

3- practice your googling skills: sometimes the problem might be very classical and it can be found on google, sometimes it can be easily found and sometimes you need to try different wording to find it so you need to practice how to search on google.

4- don't forget about oeis.org: if the problem have a single integer in input you might find the solution in oeis.org

5- keep watching blogs and comments during the contest: admins nowadays don't remove comments and blogs (or at least they don't watch them) which spoil the solution of a problem, so if you keep watching the comments and blogs during the contest you might get a solution for free

6- try out brute force solutions before the contest end: it is very often that a contest contains at least one problem which allow brute force solution either because of genernous time limit or because of weak test data

7- get used to C++ if you are not: the time limit on codeforces is the same for all languages, so if you use fast language you will have advantage over the slow languages, specially when you try to write brute force solution as mentioned in previous step

8- keep with you templates of famous data structures and algorithms: sometimes a problem on codeforces is very easy to find the correct approach, but it just needs some well-known DS which takes a lot of time to implement so if you have it beforehand you might only need to do some trivial modifications before you are ready to submit

9- also you can practice your problem solving skills, but this is not very important step compared with all the steps above