Create Dream Spark account in http://www.dreamspark.com
Go to->students section ->Click on Sign-in->Click on Create an Account->
Enter all details->Click on Verify->Select I have a verification code->Enter Dream spark key->
Click on Verify.
Now Go to App Development section and click on Windows Phone Development
Then download the sdk of windows phone 7
On the other tab go to https://dev.windowsphone.com/en-us/join and sign in with your hotmail mail account
Click on join and on the next page it will be asking you your country.
If you are a student click on the student or individual.
On the next page, you have to fill all your details correctly and click on the next button
It will be asking you the subscription whether a paid developer account for a year.
If you are a student, then go to dreamspark for which you must have linked with your hotmail account
After linking your dreamspark account with hotmail
Do select the the tab I’m a student (if you are a student) to get a free a year subscription account and click on next that’s it you got your developer account.