So, I kinda want to attempt writing a sort of Clancy-esque drama/thriller story, but the only problem is, well, I'm a pretty shitty writer. Any tips for writing in a style similar to his, or simply for writing suspense and action in general?
Read. That is the best tip anyone can get when looking to write. Don't just read one subject or author, though. Read as much as you can. It'll help you establish an identity and show you some ways to develop your own style.
In conjunction with reading as much as possible, you might also want to try some free-writing exercises. We used to do them in my creative writing courses in college to help with brainstorming and for elucidating our particular "writing voices." Wiki does a pretty good job of summing up the general exercise:
Writing within constraints is one way writers seem to produce good work. For example, character limits. Some people think twitter is a stain on writing in general, but when you're forced to work within a tight boundary, you can sometimes find yourself coming up with some cool stuff.
My advice would be: just write it anyway. It might be shitty, but you'll learn more about writing in a certain style/genre by writing in that style/genre than you will by doing anything else. Then if you can recognise what it is about your writing that's shitty you can improve on that in the next thing you write.
You could also try looking around Google for blogs or articles by published authors in that genre. I'm fairly sure Clancy himself has written some stuff about his writing process, and even if I'm remembering wrong and he hasn't I bet there are plenty who have. You'll probably find some much better genre specific advice that way than fishing for it on the RvB forums .
Maybe you could find a partner to help you out. The general plot of the book would be completely yours of course, but every few chapters you and your partner sit down together and discuss better ways of wording the story. Of course as the plot thickens, you will need to go back into earlier chapters together to check for continuity and things.
The only way to get better is to keep writing. Also, an acting coach of mine once told me that the best way to learn is to copy the masters. They are the best, after all. Eventually, you will develop your own identity as a writer.
I can only echo what everyone else is saying, but the key is to not stop! Once you get the feel for your writing, it starts to flow because your imagination is having a hay-day with ideas! As you continue writing you continue to grow on what works and what doesnt, it will take sometime but just keep pushing! The Key is to not get discouraged, and try to look at some highly successful writers and see what made them successful, Not Stephanie Meyer because Im sure she just smacked her face on a keyboard in order to write those Books from Hell! But good luck, and just keep on writing!