What Semi Formals include
For a daytime event,prefer dress pants and a collared shirt with dress shoes like oxfords or loafers.You can get some ideas by searching corporate uniforms online you will find new patterns and trends for formals as well semi formal attire.
Daytime semi formal suits can also be worn in lighter colours, like beige,but not linen suits.
For night,wear a jacket and tie,for occasions like dances or weddings.

What Not to Wear
It is easy to choose the formal attire as they are like uniforms but semi formals have some limitations as they should not look too casual for the event.Here always avoid winter or rain boots, sneakers, jeans, sportswear, baseball caps or other casual wear items.