1) Don't just sell. People have liked your page, now give them value. Let's say that you have a Pet Store.
a. Offer tips – Provide tips on how to keep animals cool in the summer or a technique on how to clean a fish bowl easily.
b. Provide general information - Introduce new products. Give links to good animal websites or videos. Provide adoption information.
c. Provide store information – Post change of hours (closing early on Saturday, etc.), a new employee with a photo (small shops are like family, introduce your new family members to the small community).
d. Entice customers to come in and shop – Provide a Facebook incentive. Post something like, "Thank you Facebook Fans – come in this week and get 10% off your purchase. Just mention Facebook at checkout to receive your discount." Or "The dog days of summer are here, bring in your dog this week and treat him/her to a large Purina bone on us."
e. Give them visuals – Post pictures of the new bunnies or fish that you have in the shop for sale. With their permission, you can post a photo of customers with their new fish, hamster, etc.
f. Solve problems - A good way to market your products/service is to show how they solve your customer's problems. "Not sure how to cut your dogs nails, here is video on how to do it gently (provide link to video). We have 7 types of nail clippers in the shop. Come on in and we'll help you with your choices." You didn't say to come in a buy. You provided solution and offered to help.
2) Don't over post. People who have liked your page can chose to hide your posts. They may still show up as liking your page, but won't see the things that you post, and there is no way for you to know if they have done that. So be careful with your content and frequency.
3) If you have a Facebook page, commit to it. The last thing you want is for people to see your page and it hasn't been updated in several months. Make sure that someone is monitoring the page. A stagnant page may translate to a stagnant business to some customers.