How to write love Shayari?

Elements of a good shayari are —

• Selection of words which makes understanding of your ashar simple for listeners
• Use of rhyming words makes it more attractive
• Way of reciting
• Emotions should be very clear in your lines
• Use of urdu ..as urdu is core of shayari

A sher is a couplet which has a meaning of it's own, and also can be part of a Ghazal, which is a collection of shers with a binding theme. A "good" sher, therefore has to have profound meaning attached to it. Like any great love Shayarii, it must transcend time and space to sound equally relevant, pleasing/shocking/saddening or however the poet intended it to be.
Example of a good sher:
Itni waaqif hain meri qalam mere jasbaaton se,
Main ishq bhi likhna chahoon, inquilab likh aati hain.

So familiar, my pen is,with my emotions,
It writes of revolution even when I write of love.

More Resources:

Romantic Love Shayari

Sad Love Shayari

Urdu Poetry