1. Keep it Simple
Don't mix up your NEEDS and your WANTS too much. If you need math materials desperately stick to those, don't add in a bunch of "fluffy" stuff. Donors do look at what you are asking for and a lot of outside donors (people you don't know) will be less likely to fund you and will move on to people who are asking for more basic necessities. That's not to say that I haven't asked for things I "want" for my classroom but its harder to get those fully funded and you lose out on the things you need if you mix them together with too much on the want side.
2. Keep the Cost Down
Requests under 500 dollars are more likely to be funded. If you can, split your projects into more than one request. For example, instead of putting 4 Chrome books on one project, split it into two separate projects. Remember that costs are added at the end for shipping, fulfillment and the optional DonorsChoose.org donation.
3. Know Your Audience
Teachers are not your target audience when you are writing up your project. Keep the wording simple and leave out all those "teachery" words like rigor, objectives, formative... you get the point. Most of your donors are going to be people outside of education who were once students themselves, so worry more about emphasizing how your project helps or inspires your students.
4. Boost Your Popularity
The more donors your project has, the more popular it will appear and more people/companies are likely to donate. Have your family or friends donate 1 or 2 dollars to your project. As little as that seems, it makes your project look more desirable to other donors.
5. Stay In the Know
There are several teacher groups and pages on Facebook dedicated to Donors Choose. Join and follow them, especially when you have a project up. This is a great way to find out about special matching events (where companies will fund half of your project if you can get the other half funded) or find people willing to trade donations. Just search "Donors Choose" on facebook to find these groups and pages.
6. Don't Give Up
For every project I have got fully funded, there is one that didn't. If you really need that iPad Mini, put that project right back up and work on the wording to make it more appealing.
7. Follow Through
When your project gets funded, make sure you follow through with your Thank You package. Post visually appealing pictures and take your time making thoughtful student thank you cards. Those donors may come back and fund your next project!