I was Destro since level 20 or so, when I figured out how to actually use talents. Before that I didn't even know what speccing meant and had random stuff all over.
I try to compare it to my other characters, but only one is past 30 yet, and he's an EZMode BM hunter.
So my only advice is.. Don't get frustrated. A destro lock has *VERY* little survivability when something goes bad. If your VW dies, and there's still more than one target left, you are almost certainly dead. Sacrifice becomes your friend, but that's almost always for running the hell away. Stam is your most important stat, followed by spell crit. I say damage comes after crit, since almost everything with crit has damage on it anyway.
It's really not that great for soloing, and it's terrible for PVP.. but it's what I play. I like how fast I can take down one target at a time, and it barely matters what demon I have out at the time. It's only there to keep them off of me for a second or two, since a normal enemy is dead in about 10.
http://www.wowarmory.com/character-sheet.xml?r=Boulderfist&n=Ehcks
For your character, though. Less spirit. You already have life tap, drain life and drain mana, while Affliction gives you dark pact and Destro eventually gives you Soul Leech. Locks have plenty of spells that decrease downtime. For everything else, keep lots of bandages. I *always* have 20 each of both levels of netherweave bandages, and plenty of extra cloth.