First of all, each and every college is very open in terms of their offerings and portfolio. All these information can be gathered via campaigns, advertisements and discussion forums (online / offline).
So here are a few data points, please note, be precise when seeking and assessing these data points for they are all fellow human beings;
1. Students - First Year
They are the best source of information on how the teaching is being done. Try to understand their transition from High School teaching to College Teaching. But please note, not everyone has the same level of understanding as you do so try to get some references to the student. Most importantly DO NOT gauge the understanding level of the student with their High School Marks.
2. Students - Final Year
These people are the white elephants amongst the students and will be having a very good insight about college. Try understanding about the facilities, placements and the importance towards the extracurricular and co-curricular activities from them.
"Sri Gurubhyo Namah"
Guru is the one who will lead you to light, the right light. Have a chat with the faculty and if possible with some senior faculty to get your doubts clarified. Be very targeted on your questions here.
They are the people who are involved in the direct working of the institution. They can be anyone from lab assistants to the drivers and they will be able to give you the right information on the subject. But not everything.
The past students from the institution who will give you a glimpse of the past. The most important metric which can be considered as a evaluation point on where the institution is now.
"Alumni are an institution's most loyal supporters."
Tip: Structure your questions accordingly when approaching them, for everyone is busy during this season and everyone has got the same amount of time..!!
Best of Luck..!!