General Cycling Discussion - Road Bike Frame Size

My height is 5'9" and my inseam is around 33". Based only on my inseam, the bike store had advised me to get a 54cm frame road bike. I am a beginner cyclist, and I heard a lot from biker friends that 54 cm might be too big for me. Any advices?

Can you ride the bike to check? The conventional wisdom about frame size is often wrong.
I see a lot of people--probably most people these days--on frames that would have been thought too small 10 or 15 years ago. In my case (I'm 6'4"), a series of shops steered me to 60 or 62cm frames for years, because that's the largest they carried. When I tried a 65cm Atlantis from Rivendell a few years ago, I was instantly more comfortable than I've been on a bike since I was a kid. There's also a belief that smaller frames are lighter and stiffer, which is technically true but not as important as fit and comfort. For that reason, I'd be inclined at least to try the larger size.
An old guideline that nobody heeds anymore, but that isn't completely useless, is to set the saddle so your leg extension is right, then close your hand around the exposed part of the seatpost. Your fist should just about hide it. If you have way more post sticking out than your hand can cover, go up a size.
You might also check with another shop or two to see what they recommend. If there's general agreement, go with their advice.

Just be careful about having the bike shop "size you" for a bike. Sometimes, they will just "ballpark" the numbers, and put you on a bike they have in stock.

In fact, you might tell them that you need them to order a bike for you. Once they do their measurements, you'll know what size you need and can choose accordingly from the bikes they have on hand. A little deceptive? Maybe, but you'll be sure you got the right size bicycle (or at least one that was selected due to your measurements and not due to what was sitting on the sales floor).

An old guideline that nobody heeds anymore, but that isn't completely useless, is to set the saddle so your leg extension is right, then close your hand around the exposed part of the seatpost. Your fist should just about hide it. If you have way more post sticking out than your hand can cover, go up a size.

This works if the frame's top tube is horizontal. If it slopes, though, then you might need half a forearm's amount of seatpost. Since so many bikes have "compact geometry" with sloping top tubes, the fistful o' seatpost guideline is, unfortunately, often useless.