Unfortunately there are no magic bullets when it comes to this wacky pursuit, it really is just a matter of trail and error. As you note there are plenty of guys here that do fantastic work, look closely at what they do, take aspects of what they do that you like and try and reproduce it in your own work. If you stick at it and keep striving for better the results will come soon enough. Its what I did, and your work is certainly better than mine when I got started.
As for a critique of your work, It appears that you have the fundamentals in place you just need to work on the details. If you want to bring some life and realism to your work pay attention to the way light and shade falls on individual objects, its rarely uniform the length of the airframe as you've drawn it. Also something to consider is they way that individual panels fit together, Look to giving the removable panels in particular stronger line and shadow. It's these seemingly trivial details that bring life to a profile.
If you want check out my fb page for an idea of what I'm talking about.
Hope this was in some way helpful.