CA state law states "Every authorized emergency vehicle shall be equipped with at least one steady burning red warning lamp visible from at least 1,000 feet to the front of the vehicle to be used as provided in this code. In addition, authorized emergency vehicles may display revolving, flashing, or steady red warning lights to the front, sides or rear of the vehicles." 25252 CVC. That's all that is technically required to go 'code 3' in CA. The rest of the vehicle code is littered with verbiage the likes of 'as may be reasonably necessary' and 'a siren shall not be sounded by an authorized emergency vehicle except when required.' In other words, the use of a siren is as much as discouraged by the CA state vehicle code, and with good reason, the PSA above shows how ineffective the siren can be. So, code 3 in CA is NOT both lights and sirens, it's merely one measly light. Now, if it's busy, I'll absolutely run with both on because IF something were to happen and you end up in court, if they ask if I was going code 3 and if I was using my lights and siren, it looks better to say yes than to have to sit and justify why I didn't have the siren sounding.
That long winded section being said. Siren use, see above, use as little as needed. You'll learn your way of doing things over time, but for me wail, or tone 1 for most of the time, then change the tone to yelp, or tone 2 when going through a red light or stop sign. Air horn as necessary and required for idiot drivers! Once, there is little to no traffic, off goes the whistles and lights only. Another note, ALWAYS at least slow to a crawl if not stop for a red light or stop sign. Can't tell you how many times I would have been killed by a dumba** driver blowing a light or sign had I not slowed or stopped. Here in CA CHP says slow to 15 mph before proceeding, but most companies are going to want a full stop.