Airplanes have entire teams dedicated to track weights.
Like Burt Rutan said when building Voyager, "If you can throw it up in the air and it comes back down it's too heavy!"
As others have said, but holes in everything from the get go. It requires a little bit of for thought, but honestly it makes robots a very distinctive look. The
robots of team 40 were a great inspiration to us as a 15+ lb overweight rookie team, they made everything light from the get go with predetermined wholes that look great, compared to our hodgepodge of holes all over our superstructure.
If you do end up overweight, it is very important to recognize that volume (and as such weight) goes with the square of the radius. A 1/2" diameter hole removes
4 times the weight of a 1/4" hole. Bring big bits.
We had a love/hate relationship with pneumatics. I think it is worth it if you use them for
several functions, but if you only need one or two things look long and hard at using motors and limit switches instead. In the two years 1276 didn't use pneumatics we came in well under the weight limit, but we also came in well under the year we used pneumatics for most of our actuators.