Most carnival games I've seen suck ass and are set up to be very hard or impossible to win. IMHO, those type of gaming operations are illegal and shameful.
If you are going to play, play at theme parks where the operations are more reputable and their goal is to have lots of winners and happy guests repeatedly playing their games.
The ladder climb game is pure skill. Some people are not athletic or balanced enough to ever win it, but some have the skill and can climb it every single time. I even know people who can walk up it on two legs without even using their hands. Since this game usually has a pretty big prize (IPODS, bikes and such) people with the skill can pretty much clean a park or carnival out. We constantly had to kick people out who were over the posted limits on wins for the season.
Ring on the coke bottle is won by tossing rings in a gentle arc so they hit the top of the bottle flat every time. Then if you toss enough rings you will eventually get one on. It might take you $3 in rings or it might take you $40, but if you can hit the bottle top flat every time your chances go up tremendously. You might also want to aim for the "bonus" prize bottle so you win something like an IPOD instead of a stuffed bear.
BB gun star shoot out is mostly luck. You have to shoot small bursts and get lucky. It's not that the barrels are bent (the guns jam if the barrel is bent) it's just that the barrels are smooth bore and shot to crap and loose and naturally are going to be inaccurate. No BB machine gun is going to shoot tight 2-inch patters, so you can be the best shot in the world and the gun doesn't have the accuracy necessary to drive tacks.
If you have kids look for the kids win every time games, or wait until it is slow and have your family play together at a race game where one of you is guaranteed to win. Just watch out for the dirtbag who will jump in at the last moment to race against your two kids and steal the win from them. I hate those guys.
The basic rule is to look at the value of the prize. If the prize is huge or otherwise valuable then the game is hard. Smaller prizes mean an easier game. Also ask for tips from the game operator. All legit games operations need to maintain a set cost of sale, just like a retail operation, so if nobody wins then nobody plays and sales go down. Legit operations also need winners walking around with prizes in hand to advertise and keep more guests playing. That's why we ring a bell or turn on a siren to advertise winners.
My personal favorite game was the high striker where you try to ring the bell with the big mallet. The old fashioned manual ones and the new electronic ones are all adjustable to make them hardier or easier to ring. When I first started working in the game I would keep it adjusted so I could just barely ring it myself. You need a baseball type swing where you get the mallet moving fast around and over your head to win. You can't just hold it up and muscle it straight down unless you are VERY strong. Big guys would get pissed if they can't ring it. I'd give them tips and show them proper technique and get them to pay for several more plays so they could win and feel good about themselves. Just good old fashioned fun, but now I'm too old and weak for that game. High Striker is the perfect example of a game where if it's too hard then nobody can win and nobody has fun and the carnival makes no money.
In the end, though, lxskllr is right. The carnival or theme park is in business to make money. It's not quite gambling, since all the games have to have an element of skill involved to be legal, but don't expect to always win unless you practice. If you aren't having fun playing the games, then go to a souvenir stand instead or save your money.