A minor is a secondary concentration of courses that often complements the major. It all depends on your interest and motivation of studying it. If you are a Computer student and have an interest in parts like maths or electronics, machines then you can take maths or communication as a minor. 

Starting a minor from the 2nd year in BTech is advicable. Minors aren't aren't worth much. There are a small number of career paths where a specific minor can help in combination with a specific major like communication with CS due to increase in fields like cloud computing and popularity and increase in technologies of 4G, 5G.

Hope it helps.