We played two campaign missions - the Intro, and Homecoming as the first side mission.

In both I was the imperial player, if found that I lost my troops very quickly and there was a number of Rebel turns when I has no imperial troops on the board, until my threat was high enough to place a new unit - which promptly got taken out.

Is this normal for the start of a campaign?

yes, that is pretty normal for the start of a campaign. Once the campaign progresses and you are getting 4, 5, or 6 threat per turn and have a few agendas and class cards under your belt, you will find that they will be much harder pressed to do that much damage and clear you out so quickly.

the beginning of the campaign Lures them into a false sense of superiority. It is up to you to learn better objective denial, and to level up. Many rebels do not know how to properly play the objective, so it is up to you to ruthlessly play your objectives. If the objective is to wound everyone, focus all of your fire on one hero until they are wounded and then ignore them. If it is to survive a certain number of rounds, husband your units and try your best to use stun and bleed to make them slow down.

Thanks for the feed back and advice, I will take note and wipe out he rebel scum

The other thing to consider is REINFORCEMENT vs. REDEPLOYMENT.

It is easier to reinforce a unit, than to redeploy them entirely, as the threat costs are generally 1/2 or 1/3 the cost of a full redeployment. There is nothing wrong with one of your stormtroopers taking cover and hiding so that you only have to spend 2 or 4 threat to get more troopers back on the board (and possibly into better positions) instead of the full 6 to redeploy the entire group.

Some things I do as the imps that seem to work:

• Clog any bottlenecks between the heroes and their objectives. If you can pile a ton of dudes around a door they HAVE to interact with, then they basically HAVE to chew through your forces to get there. All the while losing time and likely being heavily damaged...
• Focus fire on one hero at a time, making it difficult for them to rest the damage away.
• When moving, try to block line of sight from other rebels, making them have to nudge or move to attack you. Don't just stop out in the open if you could just as easily be behind some blocking terrain or another figure...
• Try to target figures that haven't activated this turn with imps that can stun or bleed - this effectively removes an action they would otherwise have. If you attack only the figures that have activated, the ones that have yet to activate will still be doing their maximum against you...

Remember that your job as the imp (most of the time) is to slow the rebels down and/or wound them all. You should be able to do both simultaneously...

Never underestimate the power of the E-Web. With innate accuracy bonus, both of its attacks (and Show of Force to make the rebels taste the rainbow), you can very easily turn an undamaged hero into a wounded hero from a decent distance.

In my experience, Ewebs die super quickly. Maybe I'm using them wrong, but I much prefer the Royal Guards and eNexu in that price range. I'm using subversive tactics so the Stun and Bleed with really well with those upgrades.

E-webs tend to die quickly, this is true.

However, if it means I wounded a hero, or at the very least, heroes channeled their attacks at it leaving other imperials unmolested, or better, rebels went out of their way to kill it, then it did its job.

Rebels learn very quickly (first mission!) that the E-Web is to be feared.

• Try to target figures that haven't activated this turn with imps that can stun or bleed - this effectively removes an action they would otherwise have. If you attack only the figures that have activated, the ones that have yet to activate will still be doing their maximum against you...

Remember that your job as the imp (most of the time) is to slow the rebels down and/or wound them all. You should be able to do both simultaneously...

This is the essence of the game: action economy. At a meta level if you can maximize your actions and limit theirs you will win.

Stun, and to a slightly lesser degree Bleed, is your great friend. Regular Royal Guards are great at this for 8 Threat.

Concentrate Fire on one Rebel at a time. A great tactic for the Imperial though, but not a fun one, is to do it again. If you've caught Mak or Jyn in the open our a fully strained Diala, and you can take them out fully, as in withdrawn, then Rebels are down 2 actions a turn which is devastating to their chances. Just keep in mind that if you have one player per Rebel, this will send them off the board until the next mission, which is poopy to do, but you're trying to win.

White dice defenders are more easily taken down than black dice. That darned Full Dodge can't come up every time, and the other side of that die is blank, with a maximum of one block.

Get Imperial Industry from the 3 Influence "Means of Production" agenda card. Stormtroopers who can Stun make things incredibly difficult for the Rebs.