My experience with paste printing so far is that it is a learned and practiced skill to make it happen well. The end goal is to have the exact right amount of paste in the exact place every single pull of the squeegee. This is simple in concept but quickly becomes a challenge as the parts become smaller and the volume goes up.
I have a rotten little printer that I modified into being acceptable. On the first day, I was definitely frustrated with alignment, thickness, and sticking issues. Over time, I have learned how to get the the printer set up just right and how to pull a print that is about 99%+ successful on fine pitch boards. It did not take long to realize that cleaning the board and pulling another print is generally faster than dealing with aftermath of a bad print. Almost all of my printing problems were fixable by human skill. The good news is that I am able to print successfully, the bad news is that I could not hire someone to take that job without a learning curve. The higher-end manual printers require less human skill. The full-auto printers require very little skill.
Some general purpose printing notes:
Take a deep breath and be prepared for unexpected details.
The squeegee is a critical part of the process - not just a flat piece of metal.
The angle and even lateral pressure is critical.
The speed of the pull is critical.
The quality of the paste is critical.
Doing a 'bubble pull' 1-2 times is important to get the bubbles out of the paste before the first print(over lexan).
There should be enough paste to roll as you pull it toward you.
Paste does not last forever, when it gets dry enough to stop rolling, it stops flowing through the apertures. Adding more paste can remedy that - adding flux is risky and I don't do that.
I wipe the bottom of the stencil after each pull with Chemwipes for fine pitch.
The stencil design is not trivial for fine pitch. If you want it to work every time - take some time to read about aperture geometry.
Supporting the stencil evenly around the PCB is important to prevent distortion of the stencil.
ENIG finished PCB's are a lot easier than HASL
In general, you can get away with violating the 'rules' for a prototype run. For production, you have to give yourself the best chance of getting it perfect every time since it is very expensive to mess up at this stage in the process.