Thanks for your suggestions :)

What you're going to want to do is, basically, use more skill. 

Honestly it is just practice and more practice. Something like SC2 though, you can watch videos of the pros and copy what they do. Though you need to learn why they do what they do and not just carbon copy, or you will never use the right moves in the right situations. So try to find ones with good announcers, as they tend to go into detail about the theory and thinking behind all the moves as they happen.

I basically fall apart if I get more than 50 units... which is why I only use ~50 units. Strike early, strike often! 

Detailed instructions for the majority of RTS games:
1) Build lots of units. Plenty of basic infantry, some tank-like things, and maybe some aircraft if available.
2) Find a nice open clearing (I like to choose somewhere close to my base)
3) Send all your units there.
4) Scroll to the location so the majority of your units are centred on the screen. Hold the left mouse button and drag from the top left of the screen, down to the bottom right. This will select all of your units.
5) If you know the location of the enemy base, right click the location on your minimap.  If you don't, send a cheap, fast unit around the map to find it before commencing step 5.
6) Repeat steps 1 through 5.
7)
 

I know usually it just takes practice. Failure only makes you better, even online.

But when it comes to RTS games how do you get better? I don't have a deep history of RTS games, I never played Starcraft 1 when it was in its prime back in the day or any other RTS. But when I do play them, i this case Supreme Commander 2 which I really like. I can't keep with all my units or manage them right.

So I guess the question is: How does one keep up with all their units in RTS games?