There are lots of people here more expert than me, but I think I'll start and then others will probably jump in and better my feeble efforts.
It is good that you tried to search first, as the requests where people didn't do that often get no answers. Did you read the stickies at the top of this and other related areas?
I saw another poster point out this segment
http://flyertalk.com/forum/showthread.php?t=566245 Worth a read.
I think I'd first figure out which program to emphasize. Any regular travel for business or pleasure that is more likely to happen, and seems more served on one airline or another. That will give you a head start on the situation. You mention NW membership so so maybe you have already made that decision.
An easy way to get more segments is to just take a trip you already have to make, and seek out the ugly routings. Lots of ways to do this, but one is just to get on the airline site itself and use the specific date option and scroll down past the direct flights.
Then get familiar with the "partners" so you know which other airlines will also credit you with segments to your chosen program. With the Delta/NW merger upon us, there likely will be changes so it will be good to check up periodically. From the school of hard knocks I learned that while Continental is a partner, when you fly on them you can only get 50% miles credited to NW. It is indeed in the fine print, but I hadn't read that far. The segment situation also has some similar kinks.
There are some rules of thumb on what constitutes a good segment price, but it really is pretty location dependent. You will figure out a good price for your area after a little experience.
Then get familiar with
http://www.farecompare.com/search/fl...by=Destination
Plug in your origin, and click on the "Total" to find out some of the cheaper runs. You can also filter for just Sky Team (left hand side). This will give you something to work with.
Then your new best friend will be matrix.itasoftware.com
This one has a steep learning curve, but it is incredible. There are instructions under the help button. The big idea though is to take a relatively inexpensive run and see if you can find options in which it has more segments, by coding in multiple airlines.
XXX(origin airport) :: NW+
YYY(destination airport) :: NW+
is a starter.
Enough for now. Try the above and get started.
Romelle