After a recent game, I helped review the turn of events with my opponent. While I was helping throughout the game and deployment, the one thing he kept wanting to do, was to move his heavy weapons. In fact, at deployment I suggested that he change his deployment and move his heavy weapons from where he had them to one of two elevated locations with good command of the field, so they could fire every round of the game. Though this might seem like common sense to the more experienced player, I still see this time and time again. I see it almost every game amongst new players, and rooks (1 and 2 years into it), perhaps because with some its becoming a habit.
Here is a little advice. You only have 5-7 rounds of play. Expect 5.
Heavy Weapons: Deploy these where they have good line of sight, and don't have to move more than once. Get down at table level, and take a look at their firing arcs (for tanks), and line of sight for infantry. Ideally they should be placed into cover, or can take a single move to get into cover. If you are moving these units 2 out of 5 rounds of the game, then 40% of the game you are not firing with them. Heavy long range weaponry, should be shooting most of the game. If you move them, seriously ask yourself why. If the reason is a good one (like get into that cover, contest that objective), then do it. Otherwise they should be performing the job they were set to do, stand and shoot.
Special Weapons (assault and rapid fire): There are a variety of ways we get these to where we want to get them. The number one rule is, keep them moving. Assault weapons tend to be meltas, and rapid fire weapons plasma guns. These should be striking your opponents where you choose. Get a move on, you don't win 40k 5th edition by standing still.
Assault Units: Mostly the same thing as your special weapons, get them to where you need them as quickly as you can. The one nice thing about assault units is for every turn you get, you get two assault phases. You also get multiple assaults. Meaning that once you do reach your opponents, it is often much easier to take out large numbers of models than would otherwise be possible with shooting. You need far less time to do your damage. Once again though, you must make sure you are always progressing these units towards your objectives or planned targets.