I've attached a PowerPoint file with the layouts I normally use. There are millions of possibilities, but these suit my style of gameplay pretty well. I use the same basic thought process for Xenonauts 1 and all of the XCom games.
As time permits and depending on how fast I get my Research Base and Engineering Base up and running I will slowly convert the default base to something more functional. I run my main strike team from here.
While that is going on I will slowly build what I call generic bases. Based on the placement of the first 3 bases I will build the generic bases in locations with the highest alien activity. From those bases, I will run additional strike teams if things get really busy. I'll load them up with fighter/interceptor aircraft with one drop ship. That being said place all of your bases for the most efficient radar coverage. Don't overlap.