When you're texting with someone, you know when it's taking "the turn." That is, they're starting to flirt, you're flirting back, and they ask:

"If you were with me right now, what would you be doing?

First, think. What exactly would you want to be doing? Don't get bashful and come back with:

"Sitting on the couch watching a movie."

You'll probably be sitting there alone. 

Like you learned in English class, get descriptive. Build the image you want them to see. From the details of where you’d like to put your hands, to where you’d like them to put their mouth. Show, don’t tell. Use the five senses. Smells are important. Talk about the "rich parade" of your lover's "hair and perfume," word to Cormac McCarthy.