You see that little dot-dottly-doo icon in the rop-right hand corner there? Ya ... that unassuming little 32x32 pixel icon just below the folder: It's the secret to reliable, manufacturable designs in Eagle! Get to know it and love it, since you'll be spending a lot of time together with it:
Learning to use the grid to your advantage is the key to quick but accurate footprint design.
There are several values here, but the only one that really matters is 'Size' and the unit dropdown box just beside it.
- Size sets the distance between each line or 'snap point' on the grid. Every new line you draw or pad you place or copy/paste will be centered on a multiple of this size. If you have a 0.65mm pitch QFN package, you place one pad at the right position, set the grid to 0.65mm, and then copy and paste the rest of the row
- Units Drop-Down: Use this to select between common engineering units (mm, inch, mil, etc.). In generall, I always use mm since every modern datasheet is based on the metric system (and yes, that's a good thing).
- Set 'Size' to 0.1
- Select 'mm' in the drop-down box right beside it
- Make sure the 'Display' radio button is set to 'On' as well so that you can see your grid
- Click 'OK'
Zoom in a bit using the scroll wheel on your mouse of the zoom icons (highlighted in the image below) until you get something resembling the zoom level below (click the image to see the grid):