I am the worst at stenciling anything. Is there sure fire technique?

Have our tried using stencil adhesive? Stenciling does talked a bit of patience and a tad bit of trial and error learned technique. Keep at it, you can do this! Here is an example.

https://www.hobbylobby.com/Crafts-Hobbies/Basic-Crafts/Glues-Adhesives/Repositionable-Stencil-Spray-Adhesive/p/29855

How to stencil, basic instructions, illustrated - Wall to Wall Stencils

https://www.walltowallstencils.com/howto/

Nothing is surefire, but some tips are use painter's tape to lock down the stencil, or use the spray on the back of the stencil. https://www.amazon.com/Stencil-Ease-Repositionable-Adhesive-Spray/dp/B008FP2RBM/ref=sr_1_3?ie=UTF8&qid=1510864482&sr=8-3&keywords=spray+adhesive+stencil

Then there is using a good pouncing brush, dipping it in paint on a plate, and then dabbing it a couple times on scrap cardboard/paper to remove excess paint. I have seen people do this with a foam brush too.

Be careful to not force too much paint around the edges so it leaks under, so start in the middle of the design and work out to the stencil edges.

Patience and practice, practice, practice....The main key is not using too much paint... better to go over twice... than have it bleed under the stencil.

There are spray adhesives that are "reposition-able" and help hold the stencil in place

https://plaidonline.com/blog/march-2014/learn-how-to-stencil-and-stenciling-tips

My first advice is PRACTICE and have patience. I use almost no paint on my brush or pounce because I can add layers if the first is too light. Either use adhesive backing spray for your stencils or use painters tape and firmly hold down the stencil as you work.