How to prepare before going to grad school I earned my Bachelor's degree in Information Technology this year and I am currently employed in the last 5 months. I am currently 20 years old and expected to be 21 when I enter graduate school.

For my background, I don't think I have something special. I barely passed during the part 2 of my undergraduate thesis. I am just a regular student back then and was not active on any organization or extracurricular activities. A kind of student who managed to pass all my subjects without failing a single unit but some of them just barely passed.

As for the job, according to my employer, on all applicants that they I have, I was the only one who was able to answer their take-home programming exam.

I am planning to take up a Master's degree in Computer Science which is somehow different from my current degree next year.

As for my research project, I haven't thought of it as of now. To be honest, I will enter the graduate school to boost my skills and credentials and also for self satisfaction.

I have roughly around 6 months more to prepare. As a student planning to take up computer science, how should I prepare in entering grad school? I don't want to waste my 6 months to do nothing and I want to prepare that bad. Is there any advice you can give me? Or something to study before entering graduate school?
Prepare financially. Grad school is not cheap. Make sure you can afford it. Even if you're going to be funded, you're probably not going to be well-paid, so the money you can save now, while you still have a job, will be precious. By having a reserve available, you can mishaps like this one since even if funding runs out you'll be able to self-fund.

Prepare a fallback plan. This ties in with #1. Do your current job well. If you manage this, then if you go to grad school and find you dislike it (happens quite a bit, e.g. see this question) you can still hopefully return to the workforce seamlessly. Perhaps you can rejoin your original employer, perhaps you can join a competitor; either way you have a lot to gain by achieving a lot in your current job. Your employer might even be willing to fund you through grad school.

Start worrying about how to find a position. After having done the two things above, start thinking about where you're going to study. Which universities are you going to apply to? Which professors do you want to work under? What topics do you want to learn? Do you want to take courses or do you want a research-only Masters? Here's where money can come in handy again, because if you're able to self-fund you'll have a wider pool of potential universities to look at.

After you've identified a university/professor, the next thing to do would be to write to read some of that professor's papers, write to that professor to make contact, possibly discuss some aspects of the intended work, and apply. If you are accepted, then you can ask the professor about what to study before attending.