Just started skullcrushers. Could you guys tell me how to properly do them?

[Blown_SC]

They're certainly a good mass-builder, as are CGBP's, JM Presses, Dips, etc...

This is slightly different than how I do them, but you get the jist of the movement. I usually bring my arms over my head a lil further...
http://www.2-fit.com/video/sklcrshr.htm

[THE CROW]

You can do them without a spotter. just put two milk crates or boxes at the end of a bench, spread out the width of your barbell or ez-curl bar. so that you can set the weight down on them without interfering with your grip. don't let not having a spotter slow you down. just adapt.hope this helps.