X-COM: Apocalypse Strategy Guide/First Week

Tactical Combat
In the first week, ammunition is scarce. There should however be enough to go around unless you waste it. However if you decide to take the guns blazing full auto approach don't expect ammunition to last. Take every possible opportunity to conserve ammunition. A few explosive grenades would be a good idea to use when appropriate. After a bio-transport module has been created fit it on a craft and try to capture live aliens. The way to do this is to attack a live specimen with a stun grenade or stun grappler until it falls unconscious, and then finish the mission before it wakes up. Throwing more stun grenades will keep it unconscious for longer.

Strategical
Put some effort in bringing down at least one of every type of UFO that appear. Also, finish the bio-transport module as soon possible and put it on a craft, the better you can start bringing in live aliens for research the better.

Strategical Combat
This early on UFO's are easy to shoot down, but it won't stay this way. Scatter your vehicles over the city so they'll have a greater chance of being close to an UFO incursion, one or two hoverbikes each should be sufficient for the early UFO's.