Here are some tips which I had follow becoming a pupil on Codeforces:

Practice: Solve problems in the 1000–1300 rating range.And learn from this problems.I highly recommended that select problems from c2ladder 1000(4), 1100(2), 1200(2), 1300(2) and create contest on Vjudge.

Understand problems: Don't submit problems until you don't understand.
1. You have to understand the problems statement,
2. read the input and output section, check the input/output constraint.
3. try to build a testcase a without watching the sample testcase.(highly recommended)
4. (if Third steps is not possible) watch the test case, and visualize the output. If your output don't match(without the constructive problems), observe the problem statement again.
5. Think the edge case.
6. don't Rush Your Journey to Success

Don't Understand problems : Don't worry, Codeforces provide their editorial for each problems.
1. Open the editorial, read First line and observe with the problem statement together.
2. If you don't understand the then move to next line until understand the problems.
3. If You understand the problems after read the editorial, then it is time to visualize the output though sample input.
4. If you don't understand the problem after read the full editorial, you should move the next problems and try it next time or rest some time and start again.

Write Solutions on IDE and Submit : After all the Problem, Write Solution on your preferred language.
1. Write solution on IDE and submit to Codeforces
2. if "Accepted!", then enjoy this problem.
3. Opps!, got WA, Think more about the possible case and write on notebook, solve using pen.(It is most important for everyone).Of course you should follow the input constraints. Make more test case and solve on notebook.And modify your solution and apply different Logic.
4. If this work, okay! Submit.Till WA, again think on the testcases.
5. After 1-hour, You can watch that test case and if this is visible, Take this on notebook or think and solve visualze the output.
6. If the output isn't visible, take some times or debug this code later. After long time, You could not think so on this problems.You can check the solution from editorals(if it is available), After reading the solution, analyze your mistakes.
7. If you understand that you can modify your solution. (don't copy-paste others code to your IDE)
8. If don't understand the editorial solution, Then check others solution form standing.
Till you can't solve this problem after watching solution,it is time to Skip this Problem.

Focus on topics: For contests and practice, focus on topics like
1. time complexity,
2. binary search on answer,
3. STL->set, map, vector priority_queue,lower_bound, upper_bound,
4. prefix sum
5. sliding window
6. two pointer.
7. Bit manipulation
(you don't need to learn advance topics)

Learn mathematics: Learn mathematics, especially forming equations, number theories, and combinatorics.

Solve problems you don't get: Try to solve problems you don't get during a real contest. Sometime you have to solve some hard problems(your rating+300) to enrich implementation.It is so useful in contest time.

You can also try these tips for beginners on Codeforces:
Participate in Division-3 virtual contests and work your way up.

Save good problems to work on later. Don't Rush Your Journey to Success.Keep practice and Compete with yourself.