Not sure how to wear a blazer with jeans? The jean/blazer look can be anything from city chic to feminine-masculine depending how you wear your blazer with jeans.
Give your blazer and jeans a textured look by adding more than one top underneath like Christie Brinkley has done. Layered two t-shirts in contrasting or complimentary shades or even add a white shirt with a crewneck sweater underneath for a menswear vibe.