3. Close Combat is Bad
Even aggressive players quickly figure out that Guardsmen simply are not cut out for Close Combat. Statistic-for-statistic, armor-save for armor-save, even the Heroic Senior Officer or Commissar is a woeful individual in the assault. The trick is to always remember this, and always stack the deck in your favor. Details about assaulting with Guardsmen will be covered in the Tactics section, but for now we'll concentrate on how your set-up should keep in mind the weakness of the Guard in the assault.
Most importantly, there is Consolidation into Combat. This rule (made explicit in the Trial Assault Rules) will force you to set up your forces at least 2" away from each other (since a base is 1" wide), and typically (to be safe) at least 3" away when looking at depth (units in front to units in back) and more than 4" away looking at width (units next to each other). Enemy units are safe from your retributive firepower when in combat, and so if they consolidate into unit after unit, you'll be unable to do much of anything to them. Keep in mind, your army is much less effective if YOU turn around and assault THEM (Guardsmen would rather be shooting). Furthermore, the Guardsmen Strength of 3 means that some enemies are entirely immune to Guardsmen attacks in combat (the Wraithlord, for example), and that in general, a Guardsman's close-combat attacks are even less effective than a Guardsman's lasgun attacks. So you want to prevent this sort of catastrophe from happening.
This is where Leadership and Morale Checks, and knowing how to make or fail them, become vitally important. The primary purpose of a screening unit is to fall back from combat in the very same turn your Guardsmen have been assaulted. The odds of your 10-man unit of Guardsmen WINNING an assault are so astronomically low against dedicated assault troops that the most you can hope for is to hurt them a little, then run and let the rest of the army take them out with their massed close-range firepower. It doesn't matter if the screening unit gets wiped out or not (although naturally if it survives and reaches your back lines, it potentially can rally and add its remaining firepower to the fray), the important thing is to stop the enemy assault and shoot the assaulters to pieces.
The second-worst thing that could happen is if your screening unit STAYS (preventing you from shooting the unit that assaulted them during your turn, and probably guaranteeing that they will wipe out the remnants of your Guardsmen in your turn, and end up free to do things on their turn again). Indeed, if you're using the Trial Assault Rules (which effectively eliminates the Sweeping Advance rules), there's actually a decent chance that your opponent will 'catch' the unit trying to flee, and keep them Locked in combat.
The WORST thing a screen can do is stay in combat even when vastly outnumbered (giving the enemy the chance to wrap around and move even closer to your other nearby units -- this will effectively render useless the "buffer" distance between units you included when setting them up, precisely to prevent Consolidation into Combat).
Remember: it doesn't matter whether you lost a screening unit or not, since if they did their job, the rest of the army can now shoot freely at the enemy next turn. Whether the enemy Sweeping Advances (original rules) or merely consolidates 3 inches, either way they are toast. After all, you did remember to keep your units separated widely enough to prevent Consolidation into Combat, right? Right?
As for intentionally trying to fail Morale checks, remember that the standard Guardsman has a Leadership of only 7. After being chopped up in combat and knocked below half strength, that's a roll of 6 or less to stay. If the survivors are outnumbered, that's an even greater chance that they'll run. The use of Company Standards or Officer Leaderships is OPTIONAL. Officers do NOT have to be inspiring or supportive that particular turn of battle, quite the contrary. You want those poor buggers that are being slaughtered by the enemy assault units to run like the blazes. It's probably the only way they'll survive, in most cases: by outrunning a pursuing enemy. Remember, if you're really lucky, the squad will still be large enough to rally in a following turn and keep shooting -- when rallying, of course, you want to use the highest available Leadership.