Bench pressing focuses on three primary muscle groups; chest, shoulders and tri's. Powerlifting form is very difficult to attain and takes alot of practice, I still don't arch my back as much as I would like.
What you need to be concernd with is keeping your elbows "tucked" and not flared out. Meaning when you lower the weight to your chest your elbows are pointing towards your feet and not away from your body. Keep them close to your side and touch the bar in the area around the bottom of your pectoral muscles.
For a grip, depending upon the length of your arms, I am 6' tall with long arms. I grip the bar with the knurl inline with my middle finger. The knurl being the smooth ring on the bar about 2/3's of the wat to the first plate from the center of the bar.
Clear as mud?? I'll check back in a bit...peace..