Above all else, believable characters can make a book believable. The events in The Hunger Games are outrageous, but we buy into the books because Katniss is so real even on the page. That's why you can't start bullying your characters in your books. You have to move them around and make them do what you want, but you've got to find ways to keep it believable. Otherwise, you're just bullying your readers, too.
You've got to make Charac Ter go to the lake, because that's where they will run into Luv Interest. But why is Charac Ter going to the lake? No matter where you're putting your character, make sure you know why they're going there. When you as the author force them there with no good reason, you're bullying the character and you're cheating your readers.
Characters have to feel like real people in order to make books believable. And real people have some motivation for doing what they do. If I'm going to the lake, I've got a good reason. Am I a photographer? A nature buff? A boating enthusiast? Give your character reasons and motivations for every action, and that's going to make them feel real. That will help the entire book feel more believable.
Don't just push your characters around. Guide them where they need to go. This will allow you to give your characters dreams, hobbies, friends, plans and interests -- all stuff that helps the character come off the page and take root in the imaginations of your readers. Don't be a bully...be a good friend to all your characters, and your readers will love your books all the better for it.