If in one gym session, I want to run (30-40 mins) and lift weights, is it better to run first or do the weights first. I have done a bunch of googling and keep reading conflicting answers so wanted to get some thoughts from folks on this forum.
You need to answer that question yourself, the way to get to it is, what is your goal? (this question to your question is taken from the great Dan John: http://www.t-nation.com/free_online_article/most_recent/figuring_out_your_life_and_lifting_goals)
Are you more focused on cardio? or strength? What are you trying to achieve? Based on your response, you can determine which to do first - the first thing to do is what is most important to achieving your goals....where you focus your most energy.
Yes, it is a question that can be complicated.
On one side, if you are practising for a running event, you should probably focus on the running first and do some complementary weight lifting.
On the other side, if you practise for general well being and have a limited time available for training, you could start with the weights and skip the running. My own experiments with measuring training effect with pulse meters shows me that you get a good cardio effect when you lift weights, especially when you do exercises that involve large muscle groups (deadlift, squats, etc).