Too much pressure!The opening lines and chapters of your book have the most pressure heaped on them to be outstanding. This is because if they're not, nobody is ever going to see the rest. Literary agents rarely want more than the first few chapters, and anecdotal evidence says they often won't read past the first few sentences if they're not immediately gripped. So the beginning of the novel absolutely has to be mind-blowing, or you've wasted the last six months, year, decade.
Not warmed up yetA lot of people take a bit of time to warm up, to get into the flow of things so their prose comes naturally, and skips along at a good pace. Often, the first few pages of writing are clunky, or even rambling. Once the writer finds their mojo though, the words fly from their fingers and onto the page, snappy dialogue, gripping action, all the good stuff.
Wanting to set the scene with too much backstoryA lot of new writers feel that they need to firmly set the scene at the beginning of a book, to let their readers know what's going on and make sure they're aware of the important plot points, where the story is going and why the lead character is acting how they are. Unfortunately, this usually has the effect of making the introduction feel like tedious exposition, where readers would rather get straight into the action.
So what can you do about it?
Start before the startBy this, I mean once you've decided where your story is going to begin, actually start writing from a scene or two earlier than that. These scenes will be cut in the end, but you will write them with full commitment as if they were staying.
By doing this, you can help avoid two of the problems described above.
Firstly, it will give you a chance to warm up and get into the flow of things.
Secondly, you will do all the exposition and backstory that your readers don't need (because they will pick everything up from context anyway, as long as your story telling is good enough).
What about reducing pressure?
Ah, yes. We haven't come up with a solution to that one yet - if anybody has any ideas - please let us know!