Basically you are suuposed to be staying there for more than the period prescribed.You must possess a ration card/voter card/any educational certifcates/etc.to be submitted along with the application form.A very easy and short cut method to acquire the domicile certificate is to submit a certificate issued by any Gazetted Officer not below the rank of Dist.collector provided if you do not have any of the above mentioned certifcates.