The Key to Elastic Demand for Hind's Katchup

The more competing products there are, the more elastic the demand is for that good. People have alternatives they can buy instead of their current choice. The better the substitutes for a good, the more willing you'll be to respond a price rise by buying something else. So my demand for some goods is elastic, and my demand for other goods is inelastic. And given this, how can i tell if something's going to be more or less elastic when it comes to my demand?