This is a question I often get asked by my clients, getting your outfits right is the key to beautiful portraits.
Dark clothes tend to slim down a person and blend better with the background meaning that the face is the focus of the photograph, which is what we are after.
Bright colours should be avoided (bright reds, pinks, greens etc) as they take attention away from the face and can become reflective and change the tone of your skin. If you are picking colours try to stick to pastels: pale blues and pale yellows work beautifully with a pair of well fitting jeans.
White can look beautiful but does not have a slimming effect, if you are not worried about this or you are of a smaller build then white fitted tops look great under a denim jacket or shirt for example.
Try to avoid prints and patterns as these can be very distracting.
It is a great idea to wear long trousers and long sleeves, this is so that the main skin on show is the face as this is where you want the viewers eyes to be drawn.
It is important that if there is more than one person in the photographs that all of the outfits blend. A good tip is to lay them all out on the bed and look at them, if your eyes are drawn to one item in particular, then this too will happen when people look at the photograph, so swap out that item for something different.
When choosing colours, you should consider whether you are going to opt for cool colours such as blues, greys, blacks. Or whether you are going to choose warm tones such as browns, greens, oranges etc. Often pastel colours are a great choice as they enhance our natural skin tones.
Don't over accessorise as this too can be very distracting in the final image. Keep hair, nails and make up simple and try to keep hair off the face as this can cause un-wanted shadows.
It is important that clothing is well fitted, on children in particular there should not be lots of 'growing room' as this doesn't look great.
I like to capture children in a natural and relaxed way, brighter colours bring out a fun side whereas white tops with jeans formalises pictures a little.
Feel free to bring any props, hats, sunglasses, blankets, comforters etc that you wish to be included in your images.
Clothing that is a 'fad' at the time should be avoided as your images will become 'out of date' very quickly.
Finally don't be afraid to dress to show your personality. If the suggestions above aren't your thing then don't worry, as they are just that, suggestions.
I hope this helps when it comes to your shoot and I look forward to meeting you!