a chaplain to join the assault marines would make them a much scarier unit! his litanies of hate are gold and ensure that your marines will actually be decent at assaulting!
more troops is always a good idea as well
oh, and never put smokes on a pred - you want to be firing evey turn! if you're really paraniod about suffering alot of glancing hits, then throw on the power of the machine spirit upgrade... (though it's best when you slap that onto a nice shiny vindicator!!!)
cheers!