Hey !
The courses you will be having in your first semester of Engineering in Computer science are :
1) Engineering Physics / Engineering Chemistry
2) Programming language (Mostly C)
3) Linear algebra
4) Advanced Calculus.
Although the names of the courses differ, the topics covered are almost same, i.e you will be having  2 Maths  papers and in most of the colleges the programming language course starts right from the 1st sem ( in some it starts at the second semester). Physics or Chemistry is the one which is present for sure.
Coming to your query, you no need to focus on Physics or Chemistry as it will mostly be a continuation of inter topics (like you will already be knowing the basics). If you are so much into programming, start with C language, go for some coaching classes (if you  are totally new to programming,  or else you may prefer self preparation)as you have mentioned preparing a language. Maths subjects also need no pre preparation.
Hope this helps
All the best !

Hey,
Hope you are doing well.
Don't be so much stressed about you first semester because first year completely is a detailed revision of what you have already studied in you class 11 and class 12.
You core subjects will be introduced in second year.
Some of the common language that you can study in your free which are related to your branch are:
1) C and C++
2) java
3) python
4) .net
Hope I made your doubts clear.
Thank you.