DS9 needs to watched in sequential order, TOS doesn't, TNG to a certain extent should be watched in order, but doesn't have to be. Some major arch's rely on character points or what has happened with say the borg.

Voyager and Enterprise aren't as sequential as DS9 but should be watched in order. There are a significant number of episodes in each you can drop from your watching order, but I couldn't tell you which ones. They both have very low points in my opinion.

As for the movies I'm sure there's a watching order. Some of the movies are very meh. If you look online you might find a good order, but if you get really into just watch them in order.