1) You have a choice of seeing the swearing-in or the parade. There is a faint chance that, if you are willing to stand around from 5 a.m. to 2 p.m. you might catch glimpses of the parade. There is no chance you will see the actual swearing-in ceremony on anything other than a Jumbotron on the Mall unless you are very well-connected. If you are that well-connected, you would not be reading my blog for advice on this.
2) They are predicting a high temperature of 31 degrees Fahrenheit on Tuesday. The daytime high is normally about 3 p.m., so it will be colder than that the entire time you will be outside.
3) Two million or more people. Five thousand port-a-potties. Need I say more?
If despite all this, you do attend, remember the cardinal rule of Washington. When taking the metro, stand right, walk left.