Throw the sheets they give you out when it comes to how to play the lanes. Use your own instincts and eyes to see what the pattern is and play it to your own ability. Just because a pattern is supposed to play at the 3rd board, doesn't mean it can't be played at the 3rd arrow etc. The lane topography, surface material, age, oil machine, oil, cleaner all play a part. The overall characteristics of the bowling center will always come through no matter what oil pattern is put out.
Knowing your own center, is half the battle in these leagues. Sheets, charts and graphs are ok when trying to point you in the direction if your bowling in a "perfect" world situation ala the PBA Tour, but sport leagues at your home center is a different story.
For instance I bowl in a PBA league where they use the same patterns 2 or 3 weeks. The 1st week I will always try to play the patterns the way they are supposed to play, or the way I've experienced them played on the regional tour. The 2nd week I will play them the way I see the lanes develop, and play the lanes how I feel they should be played for my own game. Most often than not it's in a different zone than what the "book" says, and the scores are always much higher. I'm probably 200+ the 2nd week. The 3rd week it's an evaluation of what exactly I want to learn since I'm there to learn and not score. It's normally a different ball or release in the same area where I feel the best scoring chances are for me.
I will average about 200 for the season, without really trying to score huge numbers. The goal is to learn, and get information and learn the best ways to create versatility in your game and find what works and doesn't work for you.
Your league might not allow you the flexibility in the schedule to "learn" or it might not be cost effective for you either if your bowling for money. Hopefully your league allows you to play the patterns a few times, and you can learn without the stresses of how much this practice is costing you.