David's comments should help you quite a bit. But your biggest problem, of course, is lack of experience. This will come... the main thing is to read up on sail trim, talk to other sailors, and just get as much time on the water as you can.
In your pic, the sheet to drum entry angle looks satisfactory, although I always recommend a more consistent angle, which can be achieved by mounting a turning block just before or even behind the winch drum. Your boat, like my Catalina 27 has the winches mounted on an outward canting platform that makes the entry angle pretty easy to maintain, but is a PIA when it comes to grinding (turning the handle) and cleating to avoid over rides. I've included a few pics of my set up..... this is after I upgraded to self tailing winches..... but I left the tower mounted cam cleats. They were installed by the previous owner way before I acquired the boat in 1999, and I grew to love them so much, especially when racing, I still use them even though I can cleat the sheet on the winch's jaws. The cleats were mounted on the risers to reduce the likelihood of overrides.
Okay, look at the pictures closely. The blue line is the sheet, it is not tied to the sail, rather just put in place for clarity. At the top of the picture the blue line is tied off to a stanchion (instead of the sail clew) where it runs through the movable lead block... then all the way back to heavier, stationary block that turns the sheet back towards the winch. This angle never changes and provides the line a clean entry on to the drum. I usually leave three wraps on the drum, until it's time to operate... then I add more for heavier work If I'm going to use the self tailing feature, I'll continue loading the drum all the way before setting the sheet in the jaw ring and stripper arm.
BUT...You have standard winches, which actually look like my old Barlow 2 speeds, they're really good machines, by the way. So, three wraps, then over to the cam cleat mounted on the 4 inch riser. There you go. The higher line position on the exit side is what will help you prevent over rides. With the outward canting of the winch and the super low cleat position it's no wonder you'll get so much interference causing over rides. Remember, David said to hold the line high when grinding in the new sheet, but ESPECIALLY when letting the old sheet run out....... IMPORTANT to avoid overrides on the release, pull STRAIGHT UP on the line to strip it off the drum. If you don't the low angle from the cleat will mix with the higher angled drum to lead section... thus... the override.
One more thing. If you go with new, elevated cleats, cam, clam, jam............what ever... don't use a fairlead on the cleat or anywhere between cleat and drum, or between drum and lead block. You want the sheet to NOT be CAPTIVE. It needs to run free, so you can quickly toss it off the winch.
Okey doke, I hope you pick up some perspective with this discussion. Super importantl There's a bunch of stuff you need to learn pretty quicky that will make your sailing experience much more pleasant. You'll learn to let the wind push the sail across the foredeck when tackling. Dpn't try to pull it across with the sheet, it'll likely get the clew knots caught on the shrouds. So when you tack, ease out the sheet a foot or so, as the boat turns wait for the headsail to start backwinding, it'll help get the bow through the turn more smoothly which the helmsman will appreciate. You can pull the slack out of the new sheet, but don't pull the sail until you have tossed the old sheet off the drum as I described earlier. Then hand strip the new sheet and sail into position before you start grinding the final trim position. Smooth looking and it looks salty also.
Another tip. make sure you have tell tales installed on your headsail. They're inexpensive and come with instructions. The telltales show you how the air is flowing over the sails. You can use them to adjust your sails for maximum efficiency and maintain your desired course. You can also use them to steer the boat to its optimal apparent wind angle. They also install tell tales on the leech of the mainsail. Again, the leech tells will come with instructions that tell you how to get the best "twist" on the mainsail... and other things.
I think you would appreciate learning more about sail trim, tell tales, apparent wind direction and apparent wind speed.... and how it relates to true wind speed and true wind direction.... and... how both those phenomena are related to boat speed and boat direction. If you're up for it, may I auggest picking up a copy of Don Gillette's sail trim guide, available here in the SBO store. I also recommend obtaining a copy (used or older edition is fine) of John Rousmaniere's
Annapolis Book of Seamanship. The best, IMHO.
Good luck Have fun.
