At the Tridentine Latin Mass from the 1962 missal, it is very easy to tell the difference. At the High Mass there will be six candles lit on the altar. At the Low Mass, only two. At the High Mass the prayers are mostly sung by priest, choir, and the faithful, in Gregorian Chant. At the Low Mass, the priest says the prayers, and the altar servers and the faithful respond.
At my parish, at the High Mass, our choir chants in parts–the women will sing one line, the men will sing a line, and then they sing a line together. Our priest has instructed the congregation to join in with the “together” parts of the chanting. This is how we sing the Gloria and the Credo. It is quite beautiful. The congregation also joins in with some of the spoken responses during the High Mass, also.
In our parish, at the end of Mass, we all join in with one hymn found in our old Hymnals, as Father and the 13 altar servers leave the Sanctuary.
Both types of Masses are quite beautiful and very comtemplative for me.
And for the information of another poster, yes, I do make the distinction of which priests administer our parish. There is much confusion out here between the Priestly Faternity of St. Peter (FFSP) who are loyal to the Pope; and the Society of St. Pius X (SSPX) who, sadly, for all their good intentions, are currently in schism from Rome.
Also, consider your choice of clothing. Usually folks attending a TLM dress a little more conservatively than others. Not to mean that you must wear a suit or a dress, just remember that you would dress as if you were meeting the President (as our good sisters used to say). If you are a lady, then you might consider finding a veil to wear, in case that is the norm in your area. The veils are hard to find (I had to order mine online), but don’t let the lack of a veil or the lack of a tie stop you from attending the Mass.
Mostly, you will find that everyone is quite welcoming to newcomers. If you ask, they will be happy to point out the right page for you. And you can always get your cues for kneeling and standing from the rest of the faithful.