Techniques From Closed Guard

I missed the "advanced" bjj class on Monday due to work, so I went to the later "beginner's" class. It was actually a very enlightening class because I didn't get crashed by blue belts the whole time and got to work on some techniques I have been wanting to try. The beginner's class worked on the following techniques from the closed guard:

1. Pendulum Sweep
2. Pendulum Sweep attempt to arm bar

Some observations:

1. I often take people's back but have a really tough time finishing them. Especially with guys larger and stronger than me. Their defense is to grab onto my arm and pull down preventing me from finishing the rear-naked choke or the gi choke from the back. Any suggestions would be great!
2. I'm not exactly the strongest or heaviest guy, but I need to learn how to apply my weight and pressure my opponents better.
3. I need to work on my d'arce chokes.

Till next time... ;)