One of the most important ways of learning and developing ones skills as a photographer, or indeed any other profession, is to be critiqued. Unfortunately, in the professional photography industry, there aren't that many people to be critiqued by.
It's not that there aren't plenty of people out there with an opinion, far from it! But you won't learn much if all people are doing is praising you all the time, (your mum is genetically programmed to think you're amazing!). It helps for people to say what they don't like about an image, or how they think it should be improved. It's also preferable to be critiqued by people with some form of photographic standing, especially if they're the type of person you aspire to be or work with.
I've been looking hard at my own portfolio lately with a view to improving it so I can get the clients I'm aiming for, but it's a difficult task without outside influence. We often get too close to our work. Some of our most striking images have become boring to us through over-familiarity.
So what's the answer? Well there are plenty of forums out there with millions of people willing to give their opinions. Be careful though as a lot of these people have no real photographic standing, and a lot of them will zoom in to 400% to check noise and sharpness... which is completely irrelevant! If it's a great photo, it's a great photo! There are also far too many people out on the internet who are quite happy to sit behind their keyboards and tell everyone else that they suck. Of course the important thing to remember about any form of creative medium, it's all subjective. What one person likes, another might not, so try and get opinions from several people in order to get a more balanced view.
For me, the best way to get good critique is to actually go and see people and talk to them. We live in a unique time where social media websites like Twitter and Facebook have allowed us to network with other photographers instead of being shut away in our own worlds. The trick is to turn these connections into more than just "virtual friendships". Use these people to go through your work and discuss why they like or dislike your images. How they think you could improve. What are your strengths and weaknesses etc. And in return, you can critique their work.
Over the next few weeks I'm going to be visiting several friends, whose opinions I respect, to get my work critiqued. Some of their opinions I might agree with, some I might not. What's important is that it will help to give me the direction I need to build the portfolio I need to attract the clients I aspire to.