At the start of the game you have to choose your start position.
Unless you got 2 teammates and want to rush a early scout avenger + napalm bomber against wind, your first build order is about 150 metal in early raiders and one con.
Why should you hide yourself behind your teammates?
> If they die you are dead too.
The most efficent way is it to start at the very front, send one constructor back to build mexes and spread in mostly eaqual parts near one or two metal spots at the front.
Than build really fast 2 llts to defend your base against early attacks with fleas and a radar to notice raiders who want to kill your back.
If you have a small front like on IcyRunV2, you can try to protect your base with the LLTs from your teammate on one side and protect his base with LLTs at your side.
This would be more efficient, but you cover only a little area with this way.
It isn't a good choice to take a position near the map edge unless you accept the task to save the whole economy and go Air or Gumships so you need protection from ground.
You can also choose stategic positions like ramps or hills, but build only defense buildings if you are sure that they made cost in a short time after you finished them.
Or if you really need them to save your economy and can't build ground units so early because you choose Air or Air defense if you have choosen ground.