If you want to beef up. Superset Arnies with bench press. Arnies > 3 sets of 10 as a start. Bench
A good starting weight should be one that you can lift 2 to 3 sets of 10 without feeling like it was easy. Once you find this weight, start with a set of 10 the next time you work out, then on subsequent sets add some weight to each side. It's normal to feel a little achy or sore between sets, but if you feel like your muscles are about to give out then you've gone too far.