Duders,  
 
I've been practicing with Noob mainly and I have a nice variety of BnB combos.  If I get the guy right, I can pull off some nice damage.  The trouble is that I keep having a hard time getting them started.  Sure it's easy to do against a training dummy, but real players are just always dancing or countering anything I try to set up.  Any tips?

Use more skill.

Find out which combo you can start up the fastest. i.e. which combo's first normal attack comes out the quickest so it's unlikely to be countered when that rat bastard Kung Lao is giving you his own hair trigger fast attacks. That seems to be the most logical first step since combos with slow starts can be tough to pull off if you're not combo-ing off a jumping punch to begin with.
 
Since I'm a subzero player, it's easy to start up combos against dudes that are frozen, but since almost all my normals come out painfully slow, my best defense against a kung lao player who is super aggressive and is trying to rush me down with his crazy fast attacks, is to ice slide quite a bit, since it's really quick. Sorry to take your question and run in a completely different direction with it.

this game is more about punishing wiffs than anything else. find out what the best punishment option for noob is.

though imo, noob saibot is best sitting at a long distance trying to zone fuckers out. hes not very suitable for up close engagements. you want combos that are easy to do and have millions of ways to set them up, consider playing Liu Kang. hes got great high/low mixups and has easy-mode combos. all you gotta know is b312 is your low that pop ups and 213 is your overhead that pop ups. from there you can juggle the shit outta anyone AND carry them across the damn stage into the corner where you are one mixup away from giving them a very bad day with a 15 hit corner juggle that literally is just b312 over and over again finishing with a b31 low fireball. one more mixup, and they're dead.

I have a tendency to start combos with a jump-in punch or a cross-up, and if the combo starts with a punch then I try to land the alternate punch in the air before the combo, just to help myself visualize the input.

For instance, Reptile has a normal combo that goes X, Y, Y, X (or, 1, 2, 2, 1, in fighting game vernacular). So I'll jump in with a Y-punch and then begin inputting the combo.

I tend to prioritize combos that send my opponent airborne, opening them up for a juggle, or combos that can incorporate moves that stun the opponent or lock them in place. The aforementioned Reptile combo is a great example of the former if you leave off that last X (as X, Y, Y leaves the opponent hanging in the air long enough for Reptile to let loose an Acid Ball). For the latter, Sub-Zero's Y, Y-into-Down, Forward, A is the best example. On a confirmed hit the opponent is powerless against an ice blast, allowing Sub-Zero to move in with a deadlier combo and perhaps a juggle as well.

Now, this strategy isn't fool-proof, of course. But it's a great way to start.

A lot of good input, thanks guys.  After reading some more strategy on noob, I tried actually zoning a little more and was a little more successful. 

http://www.justin.tv/s1lent1/b/285990599

54 minutes in how to play noob

this game is more about punishing wiffs than anything else. find out what the best punishment option for noob is.

though imo, noob saibot is best sitting at a long distance trying to zone fuckers out. hes not very suitable for up close engagements. you want combos that are easy to do and have millions of ways to set them up, consider playing Liu Kang. hes got great high/low mixups and has easy-mode combos. all you gotta know is b312 is your low that pop ups and 213 is your overhead that pop ups. from there you can juggle the shit outta anyone AND carry them across the damn stage into the corner where you are one mixup away from giving them a very bad day with a 15 hit corner juggle that literally is just b312 over and over again finishing with a b31 low fireball. one more mixup, and they're dead.