going to gym for the first time

hello guys,i just finished my 12th and i am planning to gym for the next 3 months until i get a college. As i am a beginner,i want to know on what basis should i choose a gym for myself,my main motive is to get in shape.I used to do a little bit of calisthenics like pushups and pullups 2 years back. Also pls give things i should keep in mind while doing gym for the first time