For concerts you need to mike everything. This means buying or renting the most powerful PA that you can afford. Run a mike to everything and run it through a mixer. You can keep the mixer on stage if you want, but it works better to have it out front so that you can adjust sound levels from the audience's point of view. As a rule of thumb, you should always put the biggest PA speakers on the outside of the stage. This accomplishes two goals: it spreads the sound out to its fullest potential; and gigantic speakers provide a dramatic backdrop for your performance and don't block the view when they are behind you.
You should always put the drums dead center of the stage on a riser. Stages are set up symmetrically around the drums. The drummer often puts on a better performance than guitarists or vocalists. The drummer also kicks off and ends songs, so everyone in the band needs to see the drummer at all times. There should also be one speaker monitor set up to one side of the drummer so he can hear the other band members.
Typically, the lead guitarist stands to the left of the vocalist. This designation has established itself as a standard concert layout. When there are two guitarists, you can put one on both sides but most often the lead stays on the left. He also puts his amp just to the left of the drummer and slightly in front within easy arm's distance if he needs to adjust it during a performance. The lead player's foot pedals, monitors and mike should also be to the left of the vocalist's mike.
The bassist is set up on the right side. Again, there's no specific reason why you can't swap bass and lead guitar, but when you try it, it seems awkward. Sound technicians have also adopted this positioning and it now comes second-hand to them. To change this standardized positioning would be detrimental, kind of like learning to drive on the left side of the road. The bassist's foot pedals, mike and monitor should also be to the right of the vocalist.
The vocalist, or "front man," is always placed in the middle. If he plays guitar, his amp should be placed on the right side between the drummer and the bass amp. The vocalist's monitor and guitar pedals should also be centered under his mike. When the lead guitarist is the prominent member of the band and the audience expects to see him first and foremost, he should be in the center.