In order to keep the team in balance, forwards need to be aware of lanes. It's really simple as you can see in the picture. Avoid being more than 2 forwards in any lane at any time, unless your forechecking with 3 forwards - trying to get to a loose puck or trying to retrive the puck in the corner.

Normally you should have a forward in every lane, both on offense and defense.

On the rush you really want to spread out and take advantage of the whole width of the ice. If the puck is loose in a corner, 2 forwards can try to win the puck while the third forward position himself in the centre lane to take advantage of offensive chances or to backcheck, if neccessary.

When backchecking there should only one forward in each lane. The defenders on the other hand should play their puck carrier. So forwards play a zone defense while the defenders play man-to-man.