It goes without saying that if you want to be a successful writer you will need learn how to set effective goals.
The obvious things, like "define your goals clearly" and "write your goals down" have already been discussed ad nauseum in zillions of blog posts all over the internet. Most readers here will already understand basic goal-setting concepts like these.
This post covers the next layer of thinking about your goals. Think of it as Goals 2.0.
1) Set a few easy goals for yourself
Some goals can be gateway goals that help you on your way to tougher goals. A goal such as I will write for 30 minutes today may seem painfully easy, but it may also help you overcome internal resistance to starting a major writing project. By motivating you to get going, easy goals can open doors to longer writing sessions and bigger writing accomplishments.
2) Get "meta" with your goals
I encourage people when they write down their goals to also write down whether a given goal helped them, and why or why not. This exercise can be particularly challenging with goals you failed to achieve. Don't berate yourself. Try to be as dispassionate as you can and honestly document what was ineffective about the goal.
When you pay close attention to which kinds of goals truly motivate you and what kinds of goals you consistently fail to reach, you can use that information to help you choose more effective goals in the future.
3) Use intermediary goals
Massive goals like I will write a novel or I will complete my PhD thesis are essentially useless if they stand alone. You will need to map out intermediary goals, along with a timeframe for each intermediary goal, in order to achieve large goals like these.
4) Experiment
Try experimenting with an extremely wide variety of goals--try using stretch goals, audacious goals, or think of fun or goofy goals that will help you maintain your motivation as a writer. There's little risk: if you pick a goal that doesn't motivate you, you can easily drop it. But be sure to keep using any goal that works well for you.
There is a talented writer inside you. Find the goals that will bring it out!