Layout your bag on a blanket (for protection). Then place you tool inside the bag and seal using the vacuum tape.
Cut a hole for your port/valve in a location that will have breather. At all times during this process, make sure your breather stays in position.
Begin applying vacuum. Making sure that the bag will not "bridge" any curves.
Bridging Bridging is what happens when there is not enough bag material to match a curve - so the bag jumps over the curve creating a high stress point on the curve and a location for resin to pool (bad).
To prevent bridging, create a location where the bag overlaps and creates a little envelope - as the vacuum presses down, it will pull this envelope apart.
Vacuum Tape NEVER allow the tape to "feel" the full vacuum. Be sure there's enough bag material near the tape to "suck down" on.