In one of my sites I just do some link building, before doing OnPage SEO.So what may be its effect ? Will I be get away from SERP ?
nah you're fine. i normally do my on page seo stuff first and then when the site is totally done i start building links. but either way, it prolly won't hurt you.
your biggest concern should be is your site ready to make money before you get it ranking. if it's not you'll miss out on potential sales.
Before starting off page optimization do on page optimization so that your off page optimization may success.