I've set up 3 or 4 commercial welding and fab shops now, and have gotten pretty familiar with the process of making the most of space available. Here's my advice.
Draw everything big to scale, then rearrange the pieces until you find something you think will work. I used CAD for this, but you can use an old school architects scale and paper if you're not familiar with CAD. I did this for all my machinery, tables and benches, toolboxes, bins and cabinets, right on down. This is a rough and quick way of getting everything in the building somewhere close to where you want it. Don't forget to consider doorways and isle-ways.
Group machines and tools by use. My mechanics tools are by the overhead door, because that's where I wrench on stuff. My welders are near the welding bench, as are the grinders and clamps. The less you have to walk to get the tools you need, the more productive you are.
Keep seldom used things or things that don't need attention out of the main areas. My air compressor is above the bathroom. I have the drain plumbed into the wash sink so I can drain it easy, and it doesn't take up floor space. Things like pallet racking and shelving can make it both easy to store seldom used things and easy to store ****. Be careful with them.
Think about what machines require what power, and if they need air. I have lots of machines that are setup for high and low voltage 3 phase, as well as 240 and 120 single phase. I was able to set up the high voltage machines such that they can take advantage of the wiring and disconnects, so I was able to save a few bucks on circuits.
You will move things around a bit until you get settled. Being able to move things with a pallet jack or forklift is a very handy thing.
To start, just get a rough idea of where you want the big stuff, and then move everything in. Then, just start putting stuff away, even if away moves a few times. It'll all fall into place.
) Chances are good that once they're gone you won't miss them, and you won't have them cluttering up the new garage.
