Study and Practice
Recap CS fundamentals
If you have been out of college for a while, it is highly advisable to review CS fundamentals — Algorithms and Data Structures. Personally, I prefer to review as I practice, so I scan through my college notes and review the various algorithms as I work on algorithm problems from LeetCode and Cracking the Coding Interview.
This interviews repository by Kevin Naughton Jr. served as a quick refresher for me.
The Medium publication basecs by Vaidehi Joshi is also a great and light-hearted resource to recap on the various data structures and algorithms.
If you are interested in how data structures are implemented, check out Lago, a Data Structures and Algorithms library for JavaScript. It is pretty much still WIP but I intend to make it into a library that is able to be used in production and also a reference resource for revising Data Structures and Algorithms.
Mastery through practice
Next, gain familiarity and mastery of the algorithms and data structures in your chosen programming language.
Practice coding questions
Practice coding algorithms using your chosen language. While Cracking the Coding Interview is a good resource for practice, I prefer being able to type code, run it and get instant feedback. There are various Online Judges such as LeetCode, HackerRank and CodeForces for you to practice questions online and get used to the language. From experience, LeetCode questions are the most similar to the kind of questions being asked in interviews whereas HackerRank and CodeForces questions resemble competitive programming questions. If you practice enough LeetCode questions, there is a good chance that you would have seen/done your actual interview question (or some variant) on LeetCode before. If you are more of a visual person, Coderust explains the common algorithm questions through step-by-step visualizations which makes understanding the solutions much easier.
Space/time complexities
Learn and understand the time and space complexities of the common operations in your chosen language. For Python, this page will come in handy. Also find out the underlying sorting algorithm that is being used in the language's sort() function and its time and space complexity (in Python its Timsort which is a hybrid sort). After completing a question on LeetCode, I usually add the time and space complexities of the written code as comments above the function body to remind myself to analyze the algorithm after I am done with the implementation.
Practice good coding style
Read up on the recommended coding style for your language and stick to it. If you have chosen Python, refer to the PEP 8 Style Guide. If you have chosen Java, refer to Google's Java Style Guide.
Internalize the pitfalls
Find out and be familiar with the common pitfalls and caveats of the language. If you point them out during the interview and intelligently avoid falling into them, you will usually impress the interviewer and that results in bonus points for your feedback, regardless of whether the interviewer is familiar with the language or not.
Broaden exposure
Gain a broad exposure to questions from various topics. In the second half of the article I mention algorithm topics and practice questions for each topic. Do around 100–200 LeetCode questions and you should be good.
Practice, practice and more practice!