In the interests of that, especially since we are seeing a bit more people actually lifting some damn impressive weights, if you and anyone else here has resources regarding avoiding injuries while lifting, let me know. I might make a 'rules of thumb to avoid hurting myself' post for next year's challenge.
I wish I had more expertise - that's why I had to consult professionals to help design a program! Plus, my injury problems are from earlier in life, and are exacerbated / triggered by lifting too ambitiously, as opposed to caused by lifting. For me, the biggest thing has been getting carried away with 'one more rep' and continually pushing past the tolerance point of my muscles, ligaments and tendons. And this doesn't have to mean a big pectoral tear. One thing I've realized more recently is that there can be a fine line between 'micro-damage that turns into gains' and 'slightly bigger damage that turns into an injury over time'.
Some people can get away with continually training to muscle failure. Particularly people who are juicing. ;) But I can't (and don't!), and it took me a long time to realize that my only sustainable gains were going to be slow gains. I'm still not quite there!
For me it was the arguably unmustachian but undeniably effective approach of:
1. Find a highly qualified trainer with proven results.
2. Follow his programming religiously (telling him things like when something was hurting more than normal, or course).
Powerlifters trend towards crazy, with many well-known ones regularly doing stupid things like training through bicep/pectoral tears. Fortunately, I found a guy who is highly qualified (backed up with his own meet results), but actually concerned about training smart, rather than just training hard. I have made ridiculous strength gains in the past 15 months with no hint of injury (as a 33 year old with some minor past back issues), so I think I made the right choice.
A couple things I have noticed that are probably worth considering for DYIers worried about injury:
1. Form trumps all. I was not allowed to lift anything resembling heavy weight until I could do it right.
2. Max effort infrequently, especially on deadlifts, especially as you get stronger. I do max effort deadlifts (usually a variation like 1-3RM off a deficit/blocks, etc.) once every 3-4 weeks at the most. The rest of the days are lower weight speed work. I go heavy on squats and bench once/week. Maxing too often will not only get you hurt, it will also slow your strength gains, so it's doubly stupid.
3. Use spotters. Self-explanatory, but so many people ignore this rule.
4. While it's important to learn to push through a certain level of discomfort, get to know your body and stop your workout immediately if you feel something twinge or give in a manner beyond normal wear and tear. This takes some experience, but I think it's fine to err on the side of caution as long as you're not being too much of a wuss. Sleep on it and reassess the next day.
5. That said, SoccerLounge is right. If it hurts a small to moderate amount, that's not always inherently bad. But if it starts getting worse, you may have a problem and it's best to rest or do alternative exercises for a while.