The Skaven view some of their ranks to be expendable, such as the Skavenslaves and Clanrats, and would happy throw 100 of their number into the fray in exchange for 1 kill. When setting up your army for battle be sure to add a meatshield of Slaves and Clanrats towards the front to soak up enemy attack, keeping your more important Skaven, such as the Lord, protected towards the back. When recruiting your army, try to keep a mix of elite units and cheap, low-tier units – use these expendable hordes to pin foes in place allowing your more elite Skaven to strike.
The only Skaven melee unit well-armoured enough to withstand a cavalry charge are the Stormvermin, so it’s best to place a couple of these towards the sides of your composition to protect from flanking – don’t worry too much about the Clanrats or Slaves, of course.
Gutter Runners are great at ambushing as they are able to move in the open without being seen by the enemy; they also have vanguard deployment so be sure to place them sneakily to soften the enemy blow before your forces meet.
The Skaven have no cavalry options, so the best practice for flanking can be found in Rat Ogres and the Doomwheel: Rat Ogres have the highest charge bonus so should be charged into the enemy wherever possible, and the Doomwheel is most effective in the flanking position. It is also the fastest Skaven unit in the roster, so place it towards the back of your army and send it in later to harass the enemy when they get close. Direct the Doomwheel into the sides of enemy units, plough through them and hastily retreat to charge again.
Place some artillery options towards the back of your army, such as the formidable Warp Lightning canon – a long-range, hard-hitting machine capable of taking out strong, single targets. If you have the gold, the Hell Pit Abomination is the absolute pinnacle of Clan Moulder’s horrifying monster-breeding program, and is too horrible to die. When death is imminent, the Abomination has a chance of either regaining some health, or releasing a pack of ravening Skaven instead. They are weak to fire though, so be sure to protect them from flaming attack where possible. Send the abomination towards heavily-armoured enemies, as its attacks are both powerful and armour-piercing.
Perhaps most important to Skaven battles is the Menace Below, an army ability allowing you to summon rats from the pestilent earth, hindering the progress of enemy units or protecting your elite units from flanking attacks. Its best used to focus your opponent’s attention where you want it – on your expendable Skavenslaves and Clanrats – and away from your more vulnerable, elite units. This ability has limited uses, but additional uses can be purchased on the pre-battle panel by expending food.
Lastly, all Skaven units get faster as their leadership decreases and even faster when they break: this makes them difficult to fully exterminate as a fleeing Skaven unit will leave the battlefield before many enemy units can catch up with them.