Your unpainted photo was very useful since it let me know it was from Reaper Miniatures and that shapes the assistance I can give. With most tabletop miniatures, you want to prime them. This tends to be done with a spray can, an airbrush, or paintable primer. Reaper Miniatures in their Bones plastic have the benefit that you can use regular acrylic paint to prime them. The downside is that you should
thin your paint and Reaper Bones are made of a material that repels water. Luckily, it doesn't do this once a layer of paint has been applied. This is one of the places where the brushes of dubious quality come in handy. Without thinning your paint, use one of the dubious brushes to spread a small amount of paint around the mini in a thin layer. This should be done quickly, which may be rough on the brush. This first coat should be either the main color of your mini or one of the common colors used for priming--black, white, grey, or brown. Doing this will fill in the plastic color so gaps in color are less obvious, like your photos.
So your first coat of paint is on the mini, now what? From here, you would use your better quality brushes, thin your paint, and carefully work on the rest of the details. Something that helps is various ways you can improve your posture. Bracing your elbows on the table and keeping your hands close makes your hands more steady. Using something like poster putty and temporarily attaching the mini to something like a pill bottle can make smaller minis more comfortable to hold. There's a lot of of things that I can't directly give advice on since I'm not where you are but I can show some examples. The earlier vid showed you how to thin your paints. I will link you to two videos on completing a first miniature--
one showing an RPG figure and the other
showing an example of drybrushing on a sci fi figure. Both use shades/washes which can be useful but not required.
Good lighting is good but for most things a simple desk lamp is fine. Or daylight. For taking photos,
here is an example of some simple tips using just a cell phone.
Ask questions if you were wondering about anything else specific.