Just a curious question: have you ever tried sketching with a pen?
Yes, but only once or twice - I never much liked pen-and-ink for anything art-related (writing is a different matter entirely - I must confess I am a little of a pen nut!), and if I had a choice I'd pick soft graphite or a similar medium over ink any day. It's partly familiarity, but also because I find it easier to express tone in graphite & co.
Why do you ask?
I ask because I highly recommend it for anyone who hasn't tried. Heck, I'm due for another round of ink in my own sketchbook.
The sketches you showed were very scribbly and were kinda difficult to decipher in places, except as silhouettes. Switching to pens for sketching will produce a lot of terrible drawings at first, but it teaches you to be more confident with the lines that you place. You know that you 1) can't erase and 2) can't use too many lines or it turns into a blob of ink, so you start to be more thoughtful and judicious with the lines that you
do put down.
Of course there's never any "right" way to do art, but that's just something I've found helpful in the past. In general I like to experiment with new media every now and again, just to keep myself from falling into a rut. It's just that the permanent nature of ink can have a very beneficial effect on the way you plan and visualize, if you let it.