Note: there are different definitions of 'success.' If you're looking for a way to get every character, attraction, token, decoration, etc., with no exceptions and no effort, then I can't help you. But I can tell you how I get the most rewards while spending zero actual dollars.
Step 1: Anticipation
Use the messages sent by Gameloft to make a note of which events are coming up when, and then be ready for them with the necessary characters and attractions in place. This is especially helpful in Gold Trophy events, when you can have your characters already on the right task when the event starts. Then when you finish the task, you've got a gold trophy hours before your unprepared fellow-Kingdomers. This has proven so successful for me that I currently have 16 gold trophies, the maximum required number plus one.
Also, when beginning a Tower Event, you can click ahead to the second and third stages to see which characters will be used. Then you can work on leveling up any characters who need a boost.
Step 2: Assessment
Once an event is revealed, you can easily see what the rewards are. All rewards are not created equal. If you already have a particular reward character in your stable, then you will be offered an Attraction Enchantment chest instead, meaning a chance to win blueprints. I don't know about you, but my blueprints multiply a lot faster than I can use them. Which means I won't knock myself out trying to win that event. Nor will I take extreme measures to score a mere Decoration Chest, or more magic (I'm currently at 35 million). I'll still participate (see Step 3), but I'll allow other tasks to take precedence over the Event.
Another thing to assess is the competition. If you start a tapper event with 10 points, and then see yourself in 49th place behind players with a hundred and ten, you know you have a pretty slim chance of winning. You could expend all your time tokens to catch up, but I'd rather save them for an event where I have a fighting chance. I'll just keep on tapping and accept a smaller prize. You won't score big every time this way, but you won't waste as many resources fighting losing battles. And just maybe those other guys spent all their tokens, leaving you a clear field for the next prize.
Step 3: Action
Get involved in every event, no matter what. If all you can score are a bunch of bronze chests, then take 'em. Who knows but you might find a gem or two. This is especially vital when Maleficent coins or any other currencies that turn into gems are at stake. Gems are your most valuable resource, so it's worth your while to participate in an event, even if that's all you'll get.
Step 4: Accumulation
Any tokens you gather but don't use are stored in the game for the next similar event. So if you've reached all the milestones in an event, it may be worth your while to collect a bunch of tokens without using them. I try to end every event with all my tokens maximized, so the next time I have to rid the park of frogs or jeweled crabs, I'm ahead of the game (see Step 1).
Those are my personal steps for success. Maybe one or more of them will help you as well.
