It's not uncommon for PAO to be overcast in the morning. When it is, it can be difficult or impossible to get in VFR, because of the hills. The most reliable time to get in VFR is in the afternoon. I generally look at the SJC and SFO TAFs, and I figure that PAO will be somewhere in between them.
If you're coming from the east, a common way to do it is to come in through Mission Pass, which is where Interstate 680 crosses over the hills from the Livermore Valley. If you have a GPS, when you call the tower, you could report your position relative to the VPKGO waypoint, which is where the three radio towers are, just north of the Dumbarton Bridge, or relative to VPSUN (Sunol Golf Course), which is nearly in the pass. Coming from the north, you could fly east of the East Bay Hills, and then cross Mission Pass. Coming from the south, it's probably easiest to call Norcal Approach for a transition of the SJC class C airspace.
You shouldn't have any trouble getting transient parking. It's near the southeast end of the ramp.