Here I'm going to share some Horde tips with the xbox.com community.
Communication and teamwork is vital! A good team will communicate what they're fortification strengthes are saving vital money in the long run. Will call out enemies and weapon pickups, etc. You can get by sitting on your own in a private party, but you won't benefit your team by not giving them vital information.
Pick a good defensive spot with your team. Another place where communication is vital. Some players will set up a Command Post anywhere, this has led to many a teams downfall and also leads to more credits being spent to establish another one.
Don't spend your money until after the first boss wave. To be quite frank, if you can't get this far without buying fortifications then you have little chance in hell later. Not spending your cash early on gives your team the chance to buy good fortifications from Wave 11+. Better teams can probably wait until Wave 21.
The Sentry's purpose falls into that of intelligence rather then offense. It alarms players when it sees something, when you activate Tac-Com you see the targets it sees, regardless of walls.
Learn the enemy spawn points. If you know where they will spawn you have a better chance of getting to them before they get to you.
Defend your defenses. Sounds a little crazy I know, but once you set up fortifications, unless you need to withdraw, try and keep the enemy away from them as long as possible. The more damage done to them the more you have to spend repairing/replacing them. Generally, try and fight just outside your defensive position.
Spot targets. Hold LT then click in the right thumbstick to mark the target. If it is killed you will earn some credits. You can also do this via Ghost Cam when you are dead and it will still earn you some credits which can help you get those few extra credits towards an extra life.
The Vulcan Cannon is a two man weapon. It should be pretty obvious but you'll be surprised how many people try and use this solo. Make sure you are not both bunched up together in case of grenades. The ammo carrier is typically defenceless so make sure to try and get him well hidden from enemy fire. Ammo carrier be prepared to tap A alot! To use this weapon effectively you need to communicate!
Learn how to use a Hammerburst. It will save you money as you can find alot of them scattered around after a wave. With being able to zoom into iron sights at the click of the right thumbstick it is also a very good weapon for accuracy. All the more important at later levels where headshots are key to downing enemies quickly.
Kill Tickers ASAP! These little ***** will destroy your fortifications very quickly if you do not deal with them. Be very vigilant!
Use Scorchers to weaken Berserkers. The amount of people who waste ammunition on Berserkers is staggering. They take very little damage if you do not burn them first. You can kill them very quickly if you use Scorchers and the environment to good effect.
Use grenades to defend. You can set grenades as proximity mines by tagging them to walls. It's not a new feature, but not many people use it to good effect! You'll be surprised how effective this can be.
Abuse the Silverback. No joke. This machine can be godly on some maps with Trenches being a great example. I've seen players use this to such good effect we may aswell have not been playing.
Abuse Shields. They are great for blocking off stairways, like on Gridlock. Slowing down Tickers and Drones alike. Use whatever you can to put a gap between them and you.
Abuse the power weapons. This is a given, if a Grinder drops a Mulcher, and it's safe to pick it up, get it. It's a stronger weapon than your rifle and saves you using your personal ammunition. There's little need to spend money on them however, though if you have a large enough reserve things like the Mortar can be useful if used effectively.
Revive team mates only when it's safe to do so. I see some people will go out of their way to get a fallen player up, but sometimes it will get them both killed. If you're going to go for a revive make sure you are backed up by other team members. Make sure there isn't a Mauler stood right next to you when you go for the revive or you're both an easy down. Sometimes it may suck for the guy who's down, and I notice in some random groups they just leave if they die, but if you die aswell then your team is down two players. Good judgment is needed here, aswell as understanding.
Have a back up plan. If you're defensive position gets overun don't be afraid to pull out and regroup. Know when to call it so that you all live to fight again.
Feel free to add any of your own.