I have watched every launch out of VAFB for the last three years and worked at SpaceX setting up SLC-4-- here are my tips for watching a launch in person.
Get there early
Get to your spot early. You don't want to be rushing to your spot five minutes before launch. I always shoot for 30-60 minutes in advance to settle and listen to launch communications. SpaceX launches draw very large crowds. After the launch it will take quite a while to exit the area.
The best launch experience is going to be on W Ocean Ave, heading as far west as you can go until the road is blocked. On the map it is marked as 'Closest Possible Viewing'. You will see spectators parking on both sides of the road. Your view will be obstructed by hills so you won't see the first two seconds of flight-- but you will get the closest possible view of the rocket in flight once it gets to about 200 feet. You will also get the most intense, chest pumping sound experience as you are only 4 miles away and the weather will likely be cool resulting in dense air.
The next best location is any of the farm roads on the nearby fields. This is the best option if you don't like crowds.
Another viewing location is Santa Lucia Canyon road which offers a partial pad view of SLC-4 (SpaceX) and a full view of SLC-3. This spot gets crowded quickly and only has limited viewing spots because of trees and shrubs. I don't recommend this spot for SpaceX launches.
My last viewing spot is at a far-away tracking station on Firefighter Road. It's good for watching the north base launches (not this one) and listening to communication traffic which they sometimes pump over a loud-speaker. There is a radiation hazard due to high power equipment. Hazard areas are clearly marked.
There are other viewing spots closer to Lompoc near Harris Grade and a park, but I never go there and know nothing about them.
Viewing Locations Map: https://www.google.com/maps/d/edit?mid=zG69-052IIE...
Listening to communications:
VAFB broadcasts launch communication traffic that can be picked up with a regular radio scanner. The frequency is 386.3 (I was also able to pick it up on 388.0 one time). You have to be within a few miles of the base. Your scanner might be offset a little, so if you don't hear anything try the nearby frequencies.
As of the Delta IV launch on Jan 12, 2018... you can still pick up launch traffic with a scanner. I have previously had trouble hearing SpaceX launch traffic on the scanner. So, your mileage may vary... but if it works, its the best way to listen.
For the launches I have listened to, when you tune in and it's broadcasting you will hear silence instead of static. This is useful for knowing if you are picking up the broadcast or not.
I personally have terrible cell connection when I'm way out watching the launch.
Maybe bring a spotting scope:
Watching the rocket prepare to return to Earth on the last SpaceX launch out of VAFB I used a spotting scope and could clearly see the rocket firing maneuvering thrusters a few minutes after launch. Perhaps you will be able to see the rocket maneuver for return...
Weather at VAFB
The Central Coast gets a ton of persistent fog June through August. It's so notable we have names for the phenomena: June Gloom, Fog-ust, etc. So, during the summer months, be prepared to see nothing-- even if it's 3 in the afternoon.
The best launches to watch
The best launches to watch are any launch within an hour after sunset or an hour before sunrise. The sky is dark but anything high up will be outside the Earth's shadow and will light up in the night sky. This scenario was the reason a recent SpaceX launch created an enormous spectacle in the Southern California sky that was visible as far as Phoenix. Do not miss these, they are somewhat rare.
Trivia and Space Landmarks around Lompoc and Surrounding Areas
If you are driving all the way up and like space, you might as well see some of the space landmarks and history in the area.
A few hours before or after the launch you can drive out to Surf Beach and get the closest direct view of the SpaceX pad.
On your way to the beach there are some neat things.
What you can see of the base
First, you will go on the same road that rockets take on their way to the pad and can see how to road was altered to accommodate. Heading west on Ocean avenue to Surf Beach, as you are almost out to the beach you will see an active military gate into the base on your left and across from it on your right is another military gate. This gate on your right is the gate that rockets being shipped to their pad will come from. Notice how there is a road with a very wide gradual turn emerging from the gate. Notice how the telephone wire is twice as high as normal over the road at this gate... this is so that wire wont interfere with satellite payloads that travel underneath. The telephone poles will be raised at various points on this road for this reason. You will drive through a cut-out hill that has notches or terraces cut into the hill. These terraces were to provide room for the wings of the space shuttle as it is towed to SLC-6 for launch. VAFB had a space shuttle complex built but the Challenger disaster stopped the west coast shuttle program. The Enterprise was brought to VAFB and setup at SLC-6.
When you get to the crest of the hill above Surf Beach you can look north on the base. The biggest buildings you see are the buildings where they process payloads in clean rooms and get them ready for launches. The rocket launches out of the north side of the base, everything north of Ocean Ave, are almost all ICBM tests aside from the very rare NASA SLC2 launch (the tall blue structure on the horizon). They take a random ICBM from a silo in the Midwest, disarm it, bring it here then launch it to Kwaj. This happens about four times a year. The south side of the base is for satellite launches. Read the Wikipedia article on VAFB, it has a very long history especially with spy satellites. In fact, SLC-4 where the SpaceX launch is coming from was the epicenter of spy satellite activity from 1963 to 2005.
A memorial for fallen astronauts (coming soon)
A neighborhood where every street is named after a rocket or astronomical object (coming soon)
Remnants of Space Tourism
Lompoc (pronounced 'lom-poke') had an economic boom and a lot of hotel construction when the space shuttle complex was built. There was an anticipation of tons of tourists. The shuttle complex fell through and Lompoc has a lot of run down hotels and other scars as a result.
Murals & Launch Posters
Lompoc has a lot of murals if you walk around downtown at Ocean and H street. There are some space murals nearby. There is a mural about the Titan line of rockets at H street and Walnut. Its a great looking mural. The McDonald's up the street on H has a mural of a man on the moon. The Lompoc DMV (interior) has some cool pictures of the shuttle on the west coast (Update: A reader reported they have been removed). Jasper's bar and Blacksmith Steakhouse (if either are still open) have lots of launch memorabilia on the walls. Usually it's posters of launches signed by the engineers. Also, and The Better Beds and Furniture store on Ocean and I has a bunch of launch posters hanging in the furniture showroom near the rear of the store.
Steak w/ Space
Your prize for reading this far is this tidbit: The coolest landmark is also a great, great place to eat. It's the Hitching Post steakhouse in Casmalia (not to be confused with the soulless touristy Hitching Post in Buellton). (HP Casmalia... http://www.hitchingpost1.com/) It is open on every day 4:30PM until 9:30PM except for on Sunday from 4PM to 9PM. This place is great because after launches the crews would come to this restaurant to celebrate. You know how old bars have photos of friends and family all over? Well this old restaurant has pictures of old space launches all over. The bathroom is plastered in launch stickers from the crews of past launches. Also, the food is amazing and this place is WAY in the middle of no-where. Its the perfect stop to go with buddies after a trip out to the area-- and it is totally, totally off the beaten path. Reservations: (805) 937-6151