First tip: don't. Writer's block is natural. Don't think that somehow it's you that's blocked. We all get blocked. Typically, when writing a novel, you'll find that you're stumped about 20,000 words into it. Sleep on in. You'll also get blocked at about 60,000 words in. It's normal.
Second tip: get organized. Make notes about who is who, and what the relationships between all of your characters are. Maybe you'll spot a connection that hadn't occurred to you before. Or maybe you'll find that you need a new character to work his way into the story.
Third tip: we do not all organize our thinking or writing in the same way. What works for me might not fit your style. I like to evolve the plot as I write. Before I started writing, I thought that writers would "sketch" their entire book out before writing it. I suspect that few people actually do this. Part of the fun of writing is making up the story as you go along.