To follow up on 1995's point that useful criticism is very difficult to obtain in any endeavor, why would songwriting be any different? Nobody (almost) has the time, energy or insight to help you with your songwriting except to teach you some terminology so that you have a vocabulary for talking analyzing songs (terms or concepts such as AABA, near rhyme, prosody, prechorus, etc.). You can learn these things from books and careful listening. Collaboration gives you an opportunity to discover the strengths and weaknesses of your co-writers and yourself. If you're lucky, you may find a level of commitment that matches your own. Writing with others will teach you things that are helpful when you write alone, too. I was in a songwriting association for a few years that met monthly and did critiques and also sponsored writers' nights. Many of the participants improved tremendously over a period of several months. Listening critically to others and making helpful comments in a supportive setting is a great process. It also helped me to become more confident about performing original music. I also learned that some of the most insightful critics were not necessarily the best writers.