Yes, you need to look up to the camera. No one looks flattering shot from the chin up 
You need a plain one colour shirt. White always looks best...unless you are doing a basic portrait, in which case most studio backdrops are white...so check that first. If it is white, then go for either caramel or powder blue (strange yes, but trust me) depending on which suits your complexion more.
Take some photos of yourself smiling on your phone, sometimes your natural smile is not your most photogenic. I'm a model, I knows my stuff, I do 
and my "prettiest" look for the camera, I feel like I'm virtually gurning!! If you want to inbox me I can tell you in quite ridiculous detail how to stand/sit etc....but you will need to practice lots, otherwise you will look like the staged/posed one whilst everyone else looks relaxed.
Make up wise, heavier eyebrows than usual, and a shit load of mascara, almost too much to wear seriously in RL...your eye makeup needs to be literally 4 times the amount you would wear normally. Don't apply this rule to all make up though, lips and cheeks must not be too rouge at all, even the tiniest amount of over blush can make you look like Mrs Rosey Apples.
Then, there are some obvious things, if you are the chubbiest family member (not mincing words here lol), don't stand directly next to the thinnest. If your face is a little on the long side, don't sit next to someone with a very round face, if you are the palest, don't stand next to the most tanned, where you will both contrast and over emphasise these things.
And always smile, lips open showing a little/lots of teeth, depending on what suits you. Teeth together or the tiniest bit parted. Never "grin" lips together, if that makes sense.