PAY TAXES BEFORE FILING RETURN OTHERWISE RETURN CAN BE BE DECLARED DEFECTIVE THEN INVALID

Your return of income shall be regarded as defective if as per explanation (aa) to section 139(9) introduced w. e. f. 01/06/2013 the tax together with interest, if any, payable in accordance with the provisions of section 140A(Self Assessment Tax), has not been paid on or before the date of furnishing of the return. 

So you have to be careful that tax if any due u/s 140A has been paid in advance before filing the return, otherwise the as per law the Assessing Officer will  considers that the return of income furnished by the assessee as defective and may intimate the defect to you and give an opportunity to rectify the defect within a period of fifteen days from the date of such intimation(If it got noticed by you as you will most likely get this intimation through mail) or within such further period which, on an application made in this behalf(If you came to know about the intimation from the Assessing Officer and make an application for extension of time to remove the defect), the Assessing Officer may, in his discretion, allow; and if the defect is not rectified within the said period of fifteen days or, as the case may be, the further period so allowed, then, notwithstanding anything contained in any other provision of this Act, the return shall be treated as an invalid return and the provisions of this Act shall apply as if the assessee had failed to furnish the return :

Provided that where the assessee rectifies the defect after the expiry of the said period of fifteen days or the further period allowed, but before the assessment is made, the Assessing Officer may condone the delay and treat the return as a valid return.