Try to have a ratio of 70% engineers to 30% scientists for best results, as well as . the Workshops to support them.
Evil Crysalid terrorists mission
When on a Terror mission that has evil Crysalid terrorists, you do not need to kill the Zombie Civilians to finish the mission. As long as all Alien forces have been defeated the mission will end successfully.
Have UFOs appear in a different country
If a UFO is spotted in a country that you do not have much for defenses or you want to lower panic somewhere else (by completing the mission to clear it), reload a previous saved game. It should still come up, but will usually be in a different location. You can continue to reload until it is in the country you desire.
Heroes
Go to the Barracks and select "View Soldiers". Select a soldier, then select "Customize". Note: This can also be done from the "Customize" menu at the "Deploy" screen. Change the name of the soldier to one of the following entries to unlock the corresponding character. Note: This will prevent achievements or trophies from being earned.
Hero
Name
Joe Kelly (Heavy)
Joe Kelly.
Ken Levine (Sniper)
Ken Levine.
Otto Zander (Assault)
Otto Zander.
Sid Meier (Support)
Sid Meier.
Panic levels
Keep Panic under control to avoid losing countries. Building satellites is one way to do this. However, choose your missions carefully and select those where the panic reduction is most needed.
Proximity bonuses
Plan ahead when building new rooms to keep the costs within reason. Having rooms of the same type next to the other usually gives you various proximity bonuses.
Re-attempting missions
If you are having problems and fail a mission, reload the auto save from the Geoscape. Select the same mission and restart. You will begin the mission with a new random map and enemy placements. This can be useful when you are out-numbered and out-gunned.
Satellites
Build satellites as soon as you can and continue to do so. They give you money monthly, and reduce panic levels. If you can fill a continent, you will get extra bonuses. The easiest continent to start with is South America.
Engineers...