Hi Wayne,
over the years, I have made a substantial portion of my income from print sales, there are good years, but most years are not so good!
One of the most important questions you need to ask yourself.....and it is a harsh question to ask is........ 'what makes me think this print will sell?'
If the answer is.....my friends and family have always told me, that I should be selling my pictures.....then I can tell you from experiance, that is not a good enough reason...
If the answer is, you have visited a few galleries and said you could take the same photograph, they are offering on the wall....that is not good enough, they already have it!
Post cards, posters, magazines, can all be productive markets to work in, although your not going to get rich, I average about .02 cents on each post card I sell, one of the most lucrative markets is the magazine and trourism industy, the yearly books they publish to entice people to come to the area and visit and spend money can be good money.
Being a successful 'Gallery artist' is difficult, there are a great number of photographers, that have come before us, that either their companies or their estates are exibiting.
I work in the magazine industry quite a bit, because, quite simply it pays! I have a number of prints hanging in galleries, but only every once in a while do they sell, not because I am not good, but because the competition is very strong.
My biggest suggestion, if you really want to sell prints, then really research the market you live in and want to exhibit in, and find out, what is selling, and find a way to take that particular niche and make it your own, either by extremely strong subject matter, or good subject matter, and extrememly strong printing skills, as has been stated, you really need to WOW the potential customer, and there is only two ways to do it!
In this day and age, the general public is inedated with images, it encircles us, and engulfs us virtually every waking hour, you just need to find a way, to use your skills and images the ones that are the engulfing ones!
I don't know that I agree, that size always matters, but if it is smaller, then it needs to stand above the pack, perfectly!
One of the quickest ways to get noticed is make big prints, frame them perfectly and make darn sure you only display the best you have to offer, no if's, and's or butt's, Period!
There are a great number of areas to explore and make sales, take a look at the endless market available to us as photographers, and you will be plesently surprised at where your income can be made at.
Dave