I struggled big time when I took up fishing as an adult and began fishing with a multiplier (Penn 500A). As a kid I only fished with a coffee grinder. I used to get an overwind at least every third cast and could only cast about 50m. I only fish 2 or 3 times a year for 3 days at a time. Things didn't improve too much and eventually I went to Kingfisher with my set up and they laughed. Set up was all wrong they said - rod tip too light. I was mad coz they sold it all to me in the first place. A year or so later I bought a 14ft Posiedon 3 (Light tip)and a Shimano speedmaster - and blow me down but things were not much better. Still casting 60 to 80 m and getting too many overwinds, burning my thumb off, etc. The good thing is that I became an expert at unpicking birds nests. Unparalleled! I persevered and picked up the following tips
1. Tighten the spool (as per what the guys are saying above)
2. Each time I cast I dip my hand in the water an sprinkle a little on the line of the spool. No more thumb burns.
3. Hook the bait onto the sinker (all the grapnel sinkers have this hook) before casting. It stops the bait from spinning and line comes off the reel much more smoothly. Bait releases from sinker on hitting the water
4. I moved to a heavier6oz sinker so I could just lob it and still get distance. It also counter-acted the tight spool.
5. I aimed to thow my bait at a point at about 75 degrees ABOVE the sea, not at the sea itself (which is at 45 degrees).
My number of owerwinds went right down but my distance was still not great with that tight spool. One tip I spent about 8 hrs throwing a plug and loosening the spoolevery once in a while. Finally I began to get some distance. Once I had the right feeling for it, I could cast the an unhooked sinker on an loose spool with very few overwinds. Hell, I can even cast my old Penn 500 with my old rod now with NO problems. Lighter sinkers or heavier sinkers (within a range of 4 to 7oz) - makes no difference to me now. I don't throw far - but I can throw over 100m if I need to, which is fine for most angling needs.
Casting is a feeling - you build fine motor muscle memory - so your body knows when to twist and your fingers when to relase and how to control that line. The right control of your thumb on that line is impossible to tell someone. It really makes no difference if you thumb the side of the spool or the line itself. Either way can work. Some guys get it quickly and others take time. I doesn't help if you are not practicing regularly. But once you have it, you have it!
BTW - Kingfisher run casting clinics every so often. I've never been to one though.
, U will get there.