And she seems to have found the recipe for success.
When you sell khao gaeng, a one-plate meal of rice with a choice of soup, curry or stir-fried items, you must first work out your customer base and then find ways to make your food unique, says the veteran copywriter.
"For instance, if you're good at cooking tamarind soup, add some cha-om [Acacia pennata] or cook it a little differently. It's also important to make your shop better known to increase the sales."
Siripun has worked at leading ad agencies such as Leo Burnett, Spa Advertising and Ogilvy, though she refuses to reveal the name of her current employer.
She warns that since ideas don't usually get approved that easily at ad agencies, you should learn to play around and change them as you go along. "You should be able to write your spiel in different tones and styles. For instance, you could practice writing it in a style that is masculine, intelligent, down to earth and poetic."
A single advertising line once kept Siripun busy from early morning until 2am while she was at Leo Burnett.
She also recommends that you have a dictionary handy.
"Open up the dictionary and point at one word. Let's say you choose the word 'black', make a story out of it. Keep doing it and you'll become good one day even though sometimes you may have to shed tears while writing," she says with a smile.
She also says that a degree in advertising isn't necessary. A lot of people in the industry are qualified in architecture or language, she adds.
"The advantages for those who've studied in a relevant programme are that they come with ideas about marketing, ad concepts and strategies."
Siripun has a degree in journalism and mass communication from Thammasat University.
She says that though some new graduates prefer to work as freelancers, she doesn't know many who have been successful at it.
"It might be okay for a while, but you can't earn a proper living from being a freelancer."
The 41-year-old also says that there's no fixed recipe for career advancement.
"Some people are both smart and good-looking and can do their job well, while others may have to work a bit harder.
"You must find out what suits you best. And the best way to survive is find your creative side - then you can win people's hearts."
By Rojana Manowalailao