What makes a good sub

I was wondering about what makes a good sub and are some good habits to maintain inside and outside of a scene. Im fairly new and a virgin so i have no knowledge whatsoever, so anything helps. Also what are some things to lookout for during a scene? I know about vetting but what are some things that are a no go or something that makes u more alert about the dom? (I know safewords are a must and hard limits but are there any other things?) Ty in advance!