• You should be at the level in which u are able to solve a medium level question in an optimized way within 35-40 mins with a clean and readable code.

1. Start solving coding question on your favorites platform like interviewbit, leetcode, gfg.
2. If you are beginner then start solving easy question 1st once you gain confidence there, go to medium and then hard question.
3. Try to solve easy question in 20 min, medium 30 min, hard in 40-50 min. its better to see the solution if u are not able to solve the question within this time frame.
4. After solving question, Try to check out solution posted by other students because sometime we can learn good trick by seeing different solutions.
5. Practice 1-10 question/day and try to maintain consistency.

• DSA itself wont be enough as you have 4 years of work exp, you should try to learn high and low system design from any free resources available on internet. 

Hope I answered your question. You can reach out to me in case of any more doubt.