Yesterday I made croissants, not from a tube, but from scratch. I learned several things through this endeavor. First, don't be stingy with the butter. I know it seems an excessive amount, but it's vital in obtaining a moist, flaky croissant.
Second, provide moisture to the area in which the dough is rising. Simply placing a cup of warm water nearby while the dough is proofing will prevent it from drying out. I hate dry bread. I often allow my dough to proof in the oven as it is warm, void of any drafts, and provides a confined space in which to supply moisture.
Finally, be patient. If you're too hasty and get rough with the dough, it will be tough. The folding and rolling becomes tedious, but taking your time, applying minimal pressure when rolling the dough out, and letting it rest in between will result in a perfect croissant.
The recipe I used came from Jacques Pepin's Complete Techniques, though there are many recipes out there for croissants. I located one here that got great reviews. Give it a try.
