Learn from my fail:
I ordered my name plate from SmartPak and received two dainty little 1/2" nails with it. I also bought a pair of needle-nose pliers to hold the nails in place and a ball peen hammer, so I wouldn't bloody my thumb and forefinger (again) with the normal sized hammer.
While I got the nails in place, and only had one bruised finger nail, I ended up missing a time or two and scratching the plate a bit.
Oh, and just after beating (begging?) the first nail into place, I realized the plate was a tick off center. Had to re-position it after removing the first nail.
-- See if you can get screws and *not* nails to mount it with. If you do get stuck with nails, you will bend one. Guaranteed. Fortunately, if you have a craft store near by (Hobby Lobby, Michael's) you can get a whole big pack of brass 1/2" nails for about $2.
-- Measure over and over and over. Use some double sided tape and put it into position so you can look at it from all angles to see how it lines up. (This is also useful for the nailing process, as a slippery saddle plate becomes a moving target.)
-- Have someone around who can lend you an extra hand or a set of eyes. If your trainer/dad/friend asks if you're OK after yelling expletives for the umpteenth time, tell them 'No. I am having trouble. Would you please help me?'
Don't just smile and try to hide your bloodied stump of a thumb.
-- If there's a store that can do it, take it to them. It seems so simple, but it's not. It's really, REALLY not.
As for the saddle and plate:
I'd get a new plate, with screws, but the scratches kind of go with the theme.