Start with Aptitude and then learn coding , there will be max 1 or 2 companies for civil ,But the Mass Recruiters will be open for all branches ,if your apti and coding will be good,you will be selected ,then move in that field only.
I won’t suggest you to prepare for GATE ,because gov/PSU jobs now a days are very very less and the vacancies which are coming are in single digits only and doing Mtech only from old IITs are worth ..even though the placement ratio (Core:Noncore) remains the same.
If you have reference ,you can get off campus or try on your own to get in some private company ,but they will pay you very less around 10–18 k per month with almost no growth and learning. Getting job in good company via off campus is also very hard