Start with a slicked back secure ponytail

Make sure your hair is off your face and free of flyaways, "whispies", etc

Use a hair net over your bun

Use pins - bun pins to keep bun in place, and flat bobby pins for loose hairs at the nape of the neck, crown of the head, etc.

Make your bun as flat and low-profile as possible 

Use hairspray or gel to make your bun secure and help with loose hairs

Just throw it up in a messy bun

Wait until the last minute

Leave loose hairs down around the face or neck

Make your bun without proper tools (bun pins, bobby pins, hair nets, brush, smoothing brush, etc.)

Make a "doorknob" bun or use things like bun makers, donuts, etc. that make your bun large or cause it to stick out far from the scalp (Bun makers are permitted for young children with very fine hair as long as you can still manage to get the bun to be low-profile)