Some good advice so far. I would add:
1) surround yourself with like minded, motivated, positive people (in the gym and in every facet of your life); positive people will lift you up, negative people will pull you down.
2) try to find someone who is where you want to be, befriend them, and ask them if they would mind you working out with them. Chances are you may need to abandon your previous prejudices, program, and may need to prove to them that you are serious about this (be prepared to get put through the ringer a little at first to see if you'll cave when pushed, but know that if you don't you'll have earned respect). This person has likely already been where you are though, and can help you to avoid a lot of the pitfalls that you may have encountered along the way to getting where they are/you want to be. Remember that there is no better teacher than experience; so try to find someone who has it.
3) In addition to mobility work, perform pre habilitation work (stuff like rotator cuff work, core stability exercises, etc...) at the end of your workout to further reduce your chances of injury
4) Keep your eyes on the prize. "Tough times don't last; tough people do." Know that no matter how well you plan or how hard and smart you train, you will run into roadblocks along your journey, everyone does. What is important is that when you do, it will ultimately fall on your shoulders to determine whether the roadblock becomes an impassible obstacle or a jumping off point to get you further towards your goal.
I realize this is all cerebral, mental advice, but to be honest, the vast, vast majority of people who have ever stepped into a gym, picked up some weights, or started exercising was capable of making drastic improvements to how their body looked, performed, and felt. What separates those who actually succeed from those who don't is more often than not dependent on what is between their ears and in their "heart".