The simplest key to winning this is to make sure you have artillery and anti-air in your deck.
Then, if you're using the original Blitz map, leave capture point A alone, and focus on putting Artillery on the ridge between B and C and a bit north.
Support some anti-air and artillery on B and your artillery/anti-air between B and C with other units until you are at max population, and just keep adding in artillery/anti-air as you lose units. It will make quick work of the waves other than the air unit waves for which you'll need a LOT of anti-air units(Reavers/Wolverines) or be quick with your leader powers.
Make sure to get all the energy crates, but watch out for the AI stealing the energy! Use fast moving units for the far away energy crates.
And, just keep spamming in artillery, anti-air, and healing units(Engineer/Nightingale).
If you have a leader power ready in your deck, you can always completely knockout an enemy wave by putting a unit near the spawn and blasting them as they spawn. The Banished Superbeam works great for this.
The advanced Blisterback is great because when it's destroyed it brings some infantry on to the map--put these on the front lines so that the infantry will act as a brief buffer.
Locusts are a great intermediate unit before you have maxed your artillery/anti-air.