Dependending on the type of information you need in your app, I too think a Facebook login can help with a quick start, like Paul mentioned.
Rewarding people for filling out their user profile also works great. Have a look at LinkedIn for example, telling you via mail or after login that you've completed 70% of your profile.
You'll be amazed what a simple badge-system will do for your users. Give them a badge for setting up their personal info (again, Facebook login!); Give them a badge for completing 5 questions, or completing all the questions on the first day of use, etc.
Reward them for inviting a friend, or linking with a friend.
But, and this is quite important too, don't be too generous. We humans actually like a challenge, so a little bit of work is actually a good thing.
If you have a set of questions in mind, group them in different categories. It's much easier to answer a set of questions in one category because you're in a particular mind set. (Personal, work related, future/goals/wishes, financial, etc)
Keep questions short and easy to answer. Yes/no, a number, no sentences.
Also, give the user a breather every now and then if you're doing numerous questions right after each other. Throw in a random funny picture, or a question like "You're on a streak! Would you like to continue for a chance to win the freezer? Yes/No" It might help having them answer a couple more questions, hoping they'll see another random one fly by.