What do we do as forwards?
*We contest the restarts that involve a scrum or a lineout
*We support ANY ball carrier by following in CLOSE support and rucking over the ball at the breakdowns
*We LISTEN to the scrumhalf and the flyhalf and do our part to execute the game plan
*We go on the offensive with pick and go's and with crash balls from the scrumhalf
*We post on either side of a defensive ruck and guard the first few channels
*We don't over commit in rucks

Here are some helpful links:

Leg drive:
A powerful leg drive is important when you go into contact and also when you tackle as a defender. Here it is demonstrated on the training pitch.
Here it is demonstrated to great effect in a match (see 1:50 minutes).

The maul:
A good maul depends on good decisions, teamwork, and practice. We should aim to form a tight wedge and get the ball to the back quickly, but in a controlled manner.
The South Africans demonstrate the perfect maul in this video (see 2:19 minutes).
Saracens don't do a bad job either.
The laws of the maul are outlined in this video.
Video on Mauling with Q&A
The important things to bear in mind are good body position and controlled movement. As you can see from the videos, the players don't rush. They are precise and controlled.

The ruck:
Most games are won at the breakdown (tackle area), if we cannot keep possesion of the ball for multiple phases, we won't win the game. Therefore, as forwards, rucking is one of our most important responsibilities (especially as the backs don't like doing it). As a team, we want to play quick running rugby and this depends on supporting the ball carrier at all times, clearing out well beyond the ball and then using it quickly to set up another phase of play. The rules and technique behindthe ruck are outlined in this video.
Powerpoint on defense at the ruck

We'll be spending a lot of time on rucking in coming practices particularly when we head outside.

The scrum:
Mike Cron Scrum Tips
Queensland Rugby Union scrum program
How to engage

For a good picture of correct body positioning in the scrum, gohere and pause the movie at 1:47 and 1:57. Notice the 6 and 8 body position is the same as the locks and front row. Square feet, knees, hips, and shoulders, back parallel with the ground, and knees bent about 100°.

All Blacks Scrum Practice Notice how fast they engage and how flat all their backs are across the top of the scrum. Clearly, the All Blacks have the most dominant scrum in rugby, but I think I see some mistakes in this video. Specifically, individuals having a large forward/backward split of their feet. They can not push to their full potential from this position. 

A bare bones construction of the SCRUM, with a checklist for each position/row. Q&A on SCRUM

Building a Safe Scrum

The tackle:
Links to Laws of the Tackle Part 1   Part 2   Part 3 for ball carrier and support players on how to navigate the tackle breakdown.
Competing at the breakdown is a good illustration of the need for support in the tackle, as well as quick attack of the ball on defense. Q&A on the tackle/ruck breakdown.