Not wanting to plug Ians book, but using it was a revaltation for me.
I was a "windmill" bowler. I ran in and bowled with by shoulder, and not even all of that, i basicall just turned my arm around in the shoulder socket as fast as I could.
Suprisingly I was (for a "village" cricketer") quite successful, being the leading bowler for my club once or twice in the late 90's and early 00's.
Then I read Ian's book. What a revalation, I now bowl "through" my chest which means supplesness and musculature in that area is actually used - something I never really understood before.
I line up my hips (so I don't bowl "around" my arse).
I use my height, I run in straight, I grip the ball correctly, and am (at the age of 40) easily a couple of yards faster than I was aged 25, and, bowling straighter, moving the ball more often.
I find myself looking at other bowlers and seeing where they are going wrong. My problem (rolling my arm over as fast as I could rather than "bowling") seems amazingly common. Second only to not sticking your chest out and bowling around your arse.
The other thing it took (despite Ians book ) was a lot of hard work practicing, running, weights, pace drills, and of course bowling, perhaps 50 overs a week - 10-12 overs a night 4 or 5 nights a week, often on my own. Bit only 6 weeks of that produced (AFAIC) really excellent results, our keeper who normally stood perhaps 4 yards back moved back to almost 10 yards, and was taking the ball comfortably at waist to chest high, and the ball was cutting off the seam 4 or 5 times an over (on a village pitch - probably wouldn't get that much on a really well prepared league pitch). Even swing now and then.
Overall, as long as back/knees hold out, I can credit Ponty's book for adding some years to me playing time - hopefully at least another 10-15 !!
(Had bike accident early October, and knees on the mend Links to my clubs website - I'm not the guy in any of the pictures btw :-) )