When knitting in the round, If you are going to SSK Stitches 3 and 4 on Round 2 of your knitting, do this for a nice, tight SSK on Round 2:
On ROUND 1, you will 'set up' the stitches for the SSK on Round 2 like this: On ROUND 1, (previous round), slip stitch no. 2, and continue knitting your round.
On ROUND 2, the SSK round, when you get to Stitch No. 2, the slipped stitch, pick up the 'bar' behind that slipped stitch with your left needle, and pull it through the slipped stitch with your right needle. You have now tightened the first stitch in your SSK. Knit the SSK stitch as you normally would.
Please refer to this excellent video by Cat Bordhi to see how the 'bar' is pulled through the slipped stitch on the SSK round:
Annie Modesitt also has a technique as well:
