I've yet to use stencils, but am waiting for the chance. If I practice too much I'll gain way too much weight.
But when I started I just winged it & they never came out like I wanted. Then I started tracing around the cookie cutter onto paper & drawing in detail. There have been cookies that I look at the cutter & say WTH? That's when I go looking for images of cookies b/c lines just seem "off" until you can see another cookie similar to what you want
For my next cookie project I'm making corset cookies for my SIL & I've had a time w/ them (the color combo is throwing me for a loop). Finally tonight I traced them onto paper & colored them w/ a marker. Taped wax paper on top, got my different RI's out & went to town. This way I was able to scrape it off & start over if I didn't like it. After about 45 min I came up w/ 3 designs I like, which will be right in front of me on Wed. This is the first time I've done this. I normally just sketch on paper, erase, re sketch, erase, resketch, etc. But I'm telling you, pink corsets w/ white & black accents is tough--one or the other not so hard.
But I love cookies, prefer them over cakes!!!! and you'll start finding inspiration on mugs (at holidays for me), plates, napkins, scrapbooking things, etc. And the more you practice the better you'll get. I'm probably the only person on the planet who does this, but I roll my own cellophane bags---like WBH does for chocolate transfers. I love it!!!! Squeeze it out when you're done & throw it away. Snip the end to be teeniny or huge. I've tried parchment & regular & disposable bags. I just don't like them as much---hate having that "pool" of icing that stays in the tip. I can get some tiny detail w/ my cello bags & I love it.
Well, I've rambled b/c I'm tired, but practice, practice, practice (on cookies or paper!)