It's easier to illustrate how *not* to do it :-)

MF, not LF, but my best portrait-style shots of small babies have been taken with them in a seat or rocker, inclined at a 30-45 angle. Not so steep that they slump, and not so flat on their backs that they get that jowly old man look. Place them on an heirloom shawl, plonk the whole lot down somewhere with even lighting, and arrange the camera so you are looking at them straight-on. Do you're best 'mad dad' look and snap while they chuckle.

For less formal shots, it helps to have a distraction. Feeding, baby massage, sleep or a machine that goes ping all help.