tl:dr; did not properly warm up shoulders, got labrum/SLAP tear.

The first piece of advice given here is to lift. This is beyond question. Consider this a PSA for your joints, tendons and ligaments. Make sure you practice immaculate form and proper warm up technique.

After lifting for years, I thought my balanced work out plan and warming up with just the bar before my main lift (warm up with light benching before heavy benching) was enough. I did not stretch or do mobility exercises for my shoulders, as light bench seemed to warm it all up enough.

I just got informed that I probably have a labrum tear from bench/incline/shoulder pressing. Despite rowing heavy and doing chin ups, I still tore it.

Do not take warming up your shoulder and rotator cuffs lightly, work all the angles and make sure you are rowing heavy and doing face-pulls with proper form (if your palms are facing the ground you might be doing it wrong, google form to double check).

I am doing a routine like this now before every session but it's too late for me to prevent this tear which will take me out of heavy upper body lifting for no shorter than 6 months. http://www.schwarzenegger.com/fitness/post/sparing-the-shoulders.

lessons learned: shoddy warm up and mobility work will ultimately put you out of service with an injury and greatly set you back. Spend 5 minutes warming up your rotator cuffs before upper body day and save yourself a lot of trouble.