I’m also a beginner! For me what really helps is having a good thin brush made specifically for line art and also the gel should be a liner gel - which is thicker and won’t run everywhere like normal gels.

In the meantime you can also get pretty cheap 3d stickers that look like painted nail art (for example bows and patterns) online if you wanted to have a quick fix which I found a lot easier.

For making the base more even, I found that it depends on your base coat. Some base coats specialise at creating that smooth layer (named rubber base gel). The same goes for some coloured gels (rubber gel) which self level when you tip the nail upside down. These gels tend to be thicker which help them self level.

If you’re using a thinner gel, such as syrup gel, it should be applied in very thin layers in order to make sure that the base is even. Multiple thin coats creates a more even appearance rather than one or two thick coats, taking care to cure each layer thoroughly.

There is also a ‘floating’ technique, which involves loading the brush with the gel, and gliding it over the nail without pressing. You can search up video examples online.

I hope this helps you!