Fun way to see the town, the tram takes you through quite a long route. The bad thing it's usually packed with tourists and it's tiring to be inside without any personal space.
I would definitely recommend starting at one end of tram route. This gives you the best chance of getting the seat/location of your choice. Even waiting at one of the starting points you aren't guaranteed to get on the first tram that comes by, but it is worth the wait to see all the sites and crawl up, down and all around Lisbon.
That was THE BEST thing I've done! Guys teach very well and know how to support, especially mentally. I was scared like never to jump but they said a few magic lines and I made it with no problem. It's quite costly, but to be honest all awesome activities cost a bit so if you want it, just do it.