Pick what to upsolve
Upsolving means solving the problems you missed after the round ends.
Upsolve the first problem you didn’t solve, and the one after it if it’s within about 300 of your rating. Past that you’ll mostly be reading. Codeforces shows each problem’s rating a little while after the round.
Also redo anything you solved after a rejected attempt. A problem you got on the third try has a bug habit in it that will cost you again.
Attempt it again first
Do it within a day or two, while you still remember what you tried. Start from the statement with a fresh 30 to 45 minute timer, as if the round were still running. A night’s sleep cracks a lot of problems that two hours of contest stress didn’t.
If you solve it, submit in practice mode and you’re done. If not, work down the hint ladder: many Codeforces editorials put hints in spoiler blocks before the solution, and the comments under the announcement often have a nudge.
Write the code yourself even after reading the editorial. Copying the author’s solution teaches you their variable names.
Read the editorial the right way
Read the editorial until the idea clicks, then close it. Most editorials state the key observation in the first few lines and spend the rest on details you can work out yourself.
Then ask why the observation is true. If the editorial says it’s optimal to sort by end time, find the swap argument, or find an input where sorting by start time fails. That reason is the part you’ll reuse on the next problem.
Read two or three accepted solutions from people near your rating and one from someone far stronger. The strong one is usually shorter, and comparing them shows you what you were overcomplicating.
Replay old rounds as virtual contests
Codeforces lets you replay any past round as a virtual contest: same problems, same length, and standings that show where you would have placed. It’s the closest thing to a real round you can run on your own schedule.
A virtual round every week or two keeps contest habits sharp between real rounds: reading quickly, testing before submitting, knowing when to move on. Run it like the real thing, full time and no editorial, then upsolve it like any other round.
For interview-style practice, Arise’s timed assessments work the same way: a fixed set, a clock and a result you can compare over time.