How to move a large group of units closely?

[Melonslise]

Whenever I attack-move each unit of a group together they will eventually form a long line because some of them get stuck and whatnot. I want all of them to move closer and wait for each other. How do I do this?

 

[Tal'Rarity]

Delayed orders or less complex terrain/pathing, and/or triggered movement.

 

[Melonslise]

Delayed orders or less complex terrain/pathing, and/or triggered movement.

I'm not sure I follow the first and the third suggestion. Can you provide a concrete example?