I recently moved in to my new home (4/1) and did quite a bit of research on this topic.
I found that the 2 step kits are the only way to go.
Just because the garage is new does not mean it is clean.
First sweep it with a push broom - be methodical to remove all dirt.
Next sweep it with a dust mop.
Then mop it. Make sure that there is no wind and the doors are closed when doing this. (I adjusted my garage doors to stay open about 6 inches when closed)
Then apply the acid wash per the instructions. I recommend that you do this on Saturday morning.
When it is dry, mop it again.
If it is hot in your area, apply the epoxy the following morning. If it is cool or if the concrete shows signs of still being wet you should wait.
Wait at least 5 days (pad a day or two more than on the instructions) before you put anything heavy on the floor.
For the first week or two I taped (using painters tape) cardboard squares to the floor where my tires sit.
These are the steps that I took and I am happy with the end product. Although I think I would do 1 thing different. I used the kit with the flakes in it (I really like the look - if you use this type make sure you take all the bags and bix the flakes together in a bucket before you apply as there are differences in each bag). Now, I would have doubled up on the epoxy to get a thicker coat. So in other words, do the prep work - apply 1st coat - let dry - apply 2nd coat and flakes.
You can kinda' see the floor in this picture:
BTW, I park on it daily (hot tires and all) without any problems. There are 2 'stains' on it now. 1 from battery acid and 1 from PVC primer.
Later,
J