Approach it as professionally as you know how. If you call to a premises in person, a shirt and tie is a must. I always carry a calculator, ultrasonic measure and notebook and pen when quoting,... I rarely use anything but the notebook,.. but it looks good to have the gear! Always submit quotes in writing, never verbally, and include your terms and conditions with the quote.
If they ask about risk assessments, method statements etc, blag your way through it,.. tell them no problem, you'll get them prepared and submit them shortly,... then run back to the forum for some help making them up!