Most GitS installments are unconnected. The only actuel sequel to the original movie is the followup movie "Innocence" which is a very different beast. You can find a complete relation graph on AniDB.
My recommendation would be to watch the "Standalone Complex" series (2 seasons + 1 special) from the early 2000's. It's top tier even though the CG does show its age. Then if you want more you could go ahead and watch the "Arise" tv show from 2015, not bad but not as good as SAC.
I would strongly advise against watching the recent Netflix-produced SAC_2045 : it's painfully bad and ugly-looking.