Where to go and what to do depends on how long you are there for, i'll assume til Saturday.
Due to the changed race schedule, there will be racing onTuesday now, if you arrive in time then it might be worth going upto the grandstand for your first view of the racing or even the bottom of bray hill. If you've never been to the isle of man it would be worht getting a mapo from the ferry or airport, then chatting to someone who either lives there or goes regularly, they will be able to mark the TT course out on the map for you, you know whenre to aim to and from then.
If you goto the bottom of bray hill, you could watch the first race then move to quarter bridge for the second race, even if you are on foot you would have time, the trick is if time is limited to leave vantage point one when maybe half the fioeld has gone through on its last lap, you then have plenty of time to get to another vantage point.

If you don't mind being stuck in the same place all day then Glen Helen is good, at the pub (1 st commentary point) or may be Ballacraine, as then you can go towards the St Johns craft centre and walk upto to watch at Ballig Bridge ( in the Glen Helen section).

If you want to combine a day out with a days racing then goto Laxey (on the coast road from Douglas to Ramsey) (early in the morning) catch the electric tram upto The Bungalow (Snaefell), you can watch the racing up there and enjoy a trip up and down on the tram, maybe ending with something to eat and drink in The Mines Tavern in Laxey? Make sure you take plenty of food and drink up with you though as it'll a full day out.
Whilst at the Bungalow don't forget you can walk over the little hills and watch at a corner before. You could if you've got transport drive upto the bungalow, watch a bit there then drive down through thol ty will glen to sulby and watch at the sulby straight and even then go through the claddaghs campsite road and watch at the Ginger hall.

Anybody who's been before a few times will point out on your map where these places are.

My eyes are Green.
ENJOY
Russ