The beginning of your book is far and away one of the hardest-working sections. In essence, it is what will either sell your book or relegate it to the Lifeline bargain bin.

As such, it's pretty important that you don't use it to introduce all of your characters like this:

Trevor was a 6'4", athletic, muscular man in his mid-thirties with brown, shoulder-length hair, hazel eyes, a scar under his left temple, tattoos on the back of his hands, an earring on each ear, a tidy goatee, faint bags underneath his eyes, and a slight limp.

He walked into the office and saw Ruby, the receptionist. Ruby was 5'6" and of average build with auburn curls, green eyes, fair skin, and a beauty spot just above her collarbone. Her torso was quite short in proportion to the rest of her ... etc.

To be clear, there's nothing wrong with giving the reader any of these details. They're all interesting things to note and give a rough idea of how the character looks. It's not about what details you give, but how you give them.

One of the problems with descriptions like the above is that as you're giving them, nothing is really happening. The characters themselves are totally disembodied, and no actions are taking place. Not only that, but the information is given as cold, hard data—informative, but bland and colourless. They effectively bring your whole narrative grinding to a halt.

This does not make for good reading.

Why not let people know about these traits with flair, right in the middle of the action? Here are some examples of alternative deliveries for some of the above details:

He frowned, tucking a stray lock of long, brown hair behind his ear.

Scratching at the scar beneath his left temple, he grunted in affirmation.

He noted a beauty spot on her collarbone, marring fair skin that was otherwise flawless.

She looked at herself in the window's reflection, cursing her disproportionate upper body.

The key here is that you don't have to deliver every little detail all at once. Such information can be staggered through the introductory scene and snuck into little events like so. It's far less invasive, much more creative, and keeps everything flowing nice and smoothly.