Polarizers. These are filters that are attached to the lens (go ahead and google. There are several different types)
Diffusers. A diffuser is anything that’s positioned between your subject and your light source in order to make the light softer and less directional. Diffusers also reduce the intensity of light.
Common diffusers include silks, scrims, nets, and grid cloths. Silks come in different weights, which determine how much they reduce the intensity of the light. Diffusers that let some light through, like grid cloths, will reduce intensity less and provide a more directional light. Diffusion cloths are usually stretched on a metal frame. Smaller diffusers are often collapsible discs.
To tone down hot spots or make lighting more even, you can use a large diffuser overhead or to one side of the scene. This is especially useful on very sunny days, when strong, directional sunlight can create harsh shadows and high light ratios on your subjects.
Reflectors. There are times when you might want to add more light, either to fill a shadow side and even out the lighting ratio, or to give a little more snap to flat lighting on an overcast day.
You can use any white or metallic surface as a reflector. Just be aware that any coloring in the reflective material will create a color cast in the light. That includes metallic surfaces that aren’t silver. Using a metallic surface will also create more specular highlights on the subject, while the light from a plain white reflector will be softer.
Common reflectors include panels and reflective fabrics stretched on frames, as well as smaller cards and collapsible discs.
Flags. If you’re dealing with an extreme available light ratio or an unwanted hot spot, you may need to completely block the light. Anything that blocks the light is called a “flag.” It’s usually made of a flat black material, so that it doesn’t reflect any light or add a color cast to the scene.
Another use for black surfaces as modifiers is to create negative fill. Just as you would set up a reflector to bounce fill light into a shadow area to make it brighter, you can set up a black surface to prevent light from bouncing onto an area to make it darker.
Common materials used as flags are black panels and Duvetyne.
Learning off camera flash and/or lighting is another option.
First learn the exposure triangle, then move on to other things.
Without learning either natural/available light modification and/or learning how to use it to your advantage, or learning off camera lighting and flash correctly, you will only make snap shots that anyone with a camera can make.
Then there’s basic composition, posing/directing, color management (monitor calibration to prepare images for print, Custom WB etc). All these basics should be learned BEFORE you open up shop. If you take on learning business at the same time as learning your fundamentals… well… you’re not doing yourself or your clients any favors.
Good Luck! I hope I helped get you started in the right direction