A common approach to shore diving is to enter, see which way the current flows & swim into it going out, then come back. But at west coast sites often current is negligible; you can dive 1 tank going one way, get out, change tanks, re-enter & go the other way, getting 2 dives at a site.
With so many sites to choose from, I'll give you a quick listing of some I'd recommend, popular dives I consider 'signature dives' (just my view). If you research sites online instead of getting a book, this might help you focus. Roughly from north to south:
1.) Karpata - lusher reef than some sites. You walk in beside a big concrete block.
2.) Ol'Blue (Tolo) - nice overall site with pretty easy entry. It & Karpata are past the 'road becomes one way' point & commit you to a long drive home, so do them together.
3.) 1,000 Steps - Sooner or later you'll want to do it. Nice site. The steps are a nice land photo op.
4.) Oil Slick Leap - I've had some really good dives here & seen neat things. It's not just good for the big giant stride entry thrill.
5 & 6.) Andrea I & II - pretty easy entries, good all around dive sites.
7.) The Cliff - not easy to figure out from the road where it is/how to get to it, but it's a small vertical wall that's fairly shallow and fun to dive.
8.) Buddy Dive's House Reef - I tend to head north, toward Captain Don's.
9.) Windsock - easy entry, plus there's a huge wooden pier that makes it easy to see where to come out when you're night diving. Good all around site. One night mosquitoes ate me alive onshore, but not every time.
10.) Invisibles - nice reef but a long swim out. Wife is sea sickness prone & tends to get sick on that swim out. Something to think about.
11.) Salt Pier - if you get past people debating whether it's open or not & whether diving it's allowed, diving along the pilings is neat.
12.) Hilma Hooker - neat dive with a double reef (a sandy 'canyon' between them) with a big wreck sitting on the sand. Swim to the far side to see tarpon. Looping around the ship I tend to hit 70 - 90 feet, so it's a deep dive & watch your air consumption. Entry & exit are marked but not the easiest.
13.) Angel City - good overall dive.
14.) Sweet Dreams - lushest reef I've seen there except maybe for Karpata.
Be mindful that far southern sites like Red Slave can have substantial current at times. Sweet Dreams didn't when I dove there, but it's near Red Slave, so be careful if you try it.
Other people will have different favorites, but those would give you a good sampler of west coast diving at popular mainstream shore sites.
Richard.
