When discussing tactics concerning the Imperial Guard people tend to always focus on talking about the puny Guardsmen or the massive tanks. Many people simply forget that the advisors exist at all! Many people think that they are not important enough to even think of including in their Imperial Guard armies. While they won't win you battles on their own they can do a large variety of roles that can help the army as a whole immensely. Let's take a look at the three kinds of advisors available to an Imperial Guard commander and take a look at the tactics at using them in the best way.
Usually orphans, these cold and stern men keep the men in line, by any means necessary. They even have the authority to execute any sergeant of officer found wanting at the front line. Below are the specific tactics employed by many a commander to make the most from these political officers. The only drawbacks of the Commissar are his it's for your only good and, to some extent his, summary execution while they both include the removal of a model, a psyker and officer/sergeant respectively, the latter includes the unit passing the test after all. Even though fluff-wise commissars are in the forefront of the action risking their lives for the Emperor the tactics detailed about using them require a certain, subtle use. Commissars should be used in a hidden way to protect themselves in order to hurt the enemy.
The Hidden Fist:
This first tactic is one of the favourite ones used by people. As commissars don't count as an independent character they cannot be targeted in assault. Thus the commissar can wield a power fist without fear of being smeared all over the ground first. Though the strength of a power fist used by a human is puny in comparison to that of, let's say, a Space Marine, forces of the Imperial Guard have always had a shortage of effective (relatively) long lasting assault personnel. Taken in a HQ unit with a Junior Officer with a Honorifica Imperialis and a power sword, and added to two or three flamers and this unit is suddenly a not half bad counter assault unit that can even take out tanks if the need arrives.
The Hidden One:
If you get the independent commissars doctrine your commissars become an elites choice, become a bit more expensive but aren't subject to the advisors rule. This means that you can get a commissar to join a unit of conscripts cheaply. Since this big bully in a large (30-40 strong) unit of poorly trained adolescents is now an independent character you should hide him. At the back of the unit is usually best but the middle is probably safer when encountering enemies of a fast nature who might strive to run round and nab your commissar. All the weapons he requires is a chainsword and a laspistol. Cheap and cheerful is the way forward here. Maybe chuck in a trademark item to make the unit even harder to break then wreak havoc with this literally fearless unit!
Priests are preachers who preach about faith in the Emperor and about the enemy are heretic scum ... stuff like that. He is an awesome warrior on the charge with his fanatical special rule and is in many peoples opinion well worth adding to your forces for some more counter assault strength. The only drawbacks with the priest is his righteous fury special rule, which effectively makes heavy weapons in the same unit useless and him not bearing the rank of officer. I guess Imperial high command doesn't think a raving lunatic who yells all day should be given such a high rank for some reason ... This means he cannot take a power fist. All is not lost however as he can take an eviscerator. While being two handed so not granting an extra attack with another hand weapon it does have excellent abilities against vehicles such as dreadnoughts. Making the priest very valuable indeed. As well, this little guy gives anyone else in the squad the ability to reroll ALL misses in close combat. Few things are a satisfying as getting some five rerollable powerfist attacks on the charge with your officer attached to a priest. There is only one real tactic that you can use with a priest ...
Ten Foot Chainsaw Massacre:
I like this tactic. It involves a priest with an eviscerator and possibly some carapace armour to protect him if he becomes the last survivor or something. Being like the commissar and thus an advisor. He does not count as an independent character. Excellent. With his two handed power fist he can pummel infantry and vehicles without fear of reprisal. Use him in a supped up HQ unit as in 'The Hidden Fist' for best effect.
People with the powers of a psyker are screened and, if they pass and are not executed immediately or used to keep the Emperor alive they will be trained and join a regiment of the Imperial Guard to aid an Officer or soldier of similar rank. These men/women with powers of the mind are probably one of the most underused advisors, if not the most underused in the codex. Barring techpriest enginseers they are seen as almost worthless by many a general. But there are cunning uses for them. Oh yes, cunning uses indeed. And being cheap it's not much of a waste if they die ... or something much worse. Such is the perils of the warp. It is advised against including a commissar in the same unit as a psyker as the it's for your own good rule can be bad for a psyker's health.
May the Force Be With You:
This is high on my cunning list. Arm your psyker with a force weapon and a Honorifica Imperialis and hide him in a close combat heavy HQ unit. The force weapon is excellent for taking out enemy heroes but remember that while the psyker is an advisor and thus not an independent character he is not very strong or skilled with his weapons. Use him wisely.
Luck of the Dice Gods:
Just get a normal psyker and plonk him in an HQ unit. Pray that the dice gods are kind and give you a useful power. Use him in the way his power (if he even has one) dictates what he should be doing. Standing around doing nothing with telepathic order for example.
Though these are just some of the uses of Imperial Guard advisors, it's easy to see that these can be, in the least, an interesting add-on to any Imperial Guard command squad.