Question: I have read your page on the 'Sagging Middle' and I have followed all your steps and almost have a complete story plan, but whenever I get down to actually write the thing, I get stuck. I can write about fifty or so pages but after that I get bored with my current novel and start a new one (normally without planning) but I am serious about this one. Is there any help or advice you could offer for writers block? All help would be really appreciated, thanks!
Most writers go through this. Middles are tough. In fact, you could argue that the discipline to get through the middle is what separates "the men from the boys" in the writing game, if you can forgive the sexist metaphor.
If you have a good outline, you have taken an important step. You know where you are going with the story. Just focus on one event at a time. Conjure the feeling of the next step in your story and write it fully. Then move on. Once you reach the point where the end is in sight, it gets easier.
The other thing that can help is to write very quickly. If this were autumn, I'd recommend you participate in Nanowrimo, which is a writing challenge held each November, in which you write 50,000 words of a novel in 30 days. (This works out to roughly 1,700 words a day, which most people can do in a couple of hours if they don't stop to revise and censor themselves.)
You can set up a similar challenge for yourself with a deadline and daily accountability. Arrange rewards along the way that you will only get if you reach your goal. (E.g. have your partner agree to give you a massage if you reach your weekly goal, swear off TV, internet, or alcohol until you're finished, arrange a night out with friends or buy yourself a treat when you're done, etc.)
While you're doing this program, give yourself permission to write badly. Hold off all editing, revising, etc. until after the deadline has passed and you've finished a complete draft. The challenge is just to get as many words down as possible in a short time. It's about quantity, not quality.
It also helps to have a set time to start each day. Let the rest of the household, friends, etc. know that you will start at a set time each day and will not allow interruptions, answer the phone, emails, etc. until you've hit 1,700 words.
Best of luck.