Proposed newbie watching order
1. Movies. The movies are designed for the widest audience and therefore the most accessible, so start there:
Star Trek II
Star Trek III
Star Trek IV
Star Trek VI
2. Original Series. If still interested, then go to the original Star Trek series.
Watch all except, if you want, skip anything rated less than 6.0 on IMDB.
3. The Next Generation. Then go to The Next Generation.
Watch all seven seasons or else you might miss certain developments.
4. Voyager. After that, if you want to keep watching, switch over to Voyager.
Voyager is the most like Trek-like series to watch next.
5. Enterprise.
Enterprise is the next most interesting series. One would like to tell you to skip episodes rated lower than 6.0, but you would probably miss something important.
6. Deep Space Nine.
So different from normal Trek that you could call it Anti-Trek. But check it out in case you like it.