With RSRD, think historical. Doesn't hurt to complete your patrol zone, but don't feel obliged to stay there hunting.
Stay in shipping lanes and try to find narrow straits where you can bottleneck them.
Early war think invasion forces. That's why I prefer starting out of Manila and moving down south. Many large invasion forces hit the Philippines at the start of the war. Then Feb/March you can find several large invasion forces hitting Borneo, then Java. You'll run into large convoys of 30-50 ships.
Don't forget the historical battles. Some are easy to find, others not so easy, but they're all in RSRD. Here's a good map for battles, just click a battle to the left then view battle animation. I prefer to cut TF off at points before the actual battle took place. Check out the Jap onslaught for idea's where invasion forces land, you can almost look at the animation and compare it to the SS in the bottom link and are identical.
Again, starting out of Manila, I'll head North and attack the invasion fleet at Vigan and Ling. Gulf. You'll lose Manila, so head to Surabaya. I'll then attack all the invasion forces hitting Java late Feb and early March. After that, you have to move to Fremantle, but I port at Brisbane as soon as it becomes available. I then partake of the Battle of the Coral Sea. I may even take the trip and do Midway, but usually stay in the Solomons. I'll stay in the Solomon's most of 42, just stay in the slot and you'll run into stuff about every night. Love the Bismark Sea in 43.
http://www.historyanimated.com/pacificwaranimated/
Here are some SS's showing locations of battles, invasion forces and convoys with RSRD.
http://www.subsim.com/radioroom/showthread.php?t=159862