(bake) texture problem with Blender when creating cc

Hi. We would need to see what’s going on in your blend, but in short, your are baking an ambient occlusion, not materials to texture. Imagine blender creating a glowing white sphere around your object that lights it from all angles. That is ambient light. When there is a sleeve, the light that is coming from above the sleeve will meets an obstacle(the sleeve), the area below the sleeve on the torso receives less light than the chest, for example, that is not obscured by anything. What this person does wrong is delete the body. You should also be adding the floor because clothing does not float in the void, it exists on the body, it has the body casting shadows on it, it has the light bouncing from the ground, etc.
Basically, if you want to bake the black material with a specular map and all, you bake that as Combined, preferably in Cycles.
If you want to add some complexity to your existing textures, do not delete the body and add the floor plane.
If this will not work, share the blend file please, you might have too much light in the scene

It's been a few hours since your post so I'll go ahead and answer, though Mauvemorn is the one who knows the most about these things. Everything I've learned has been from her.

First, your polycount is way too high. Use the decimate modifier to lower it. Decimate ruins the topology but in this case, MD has already ruined your topology so you have nothing to lose. And speaking of MD, model in quads and keep your particle distance high. Don't worry about body parts clipping through if you know you'll delete those body parts later (any body parts covered by your mesh).

An ambient occlusion map is a shadow map. You're baking shadows onto your mesh so it doesn't look flat. Ambient light is light that exists everywhere in your scene; it doesn't come from a source such as a lamp so delete all of the lamps in your scene. Occlusion is just when something is blocking something else. Sort of like if you put your hand under a lamp the top of your hand would be lit up but the bottom would be in shadow because the bottom of your hand has been blocked from the light. Blender calculates the light that exists and what's blocking the light and then bakes those shadows onto a texture. This occlusion part is why Mauvemorn says to put a "floor" under your sim. This helps Blender to better calculate how light interacts with your mesh.

I had some trouble at first baking shadows onto your map and it was because you have materials assigned to your mesh. There might be a better way of fixing this but I just ended up deleting the black material. You don't need to have a material assigned to your mesh; you'll make your diffuse in Photoshop and import it to Studio. I unchecked Normalize, as well. Got a pretty decent bake. Export your baked ambient occlusion map via the UV editor. Image > Save as Image or the shortcut F3. Open your ambient occlusion map in Photoshop, and do what you need to do to add color/texture.

Thank you so much both you guys!!
I'm a beginner to all these so I'm still struggling through the steps unfortunately, but what I have now looks so much better than before! I'm pretty satisfied with anything at this point honestly.. :')
Is there a way for me to look into the finished files that you made with my cc?
I thought I deleted the body pretty thoroughly but I'm still seeing these little cracks on the body when I try to export in S4 Studio..:(

image

Wow, thank you so much for such thorough instructions!!
I might be able to do much better job on my next cc keeping in mind all of those:)
But could you help me with one more thing?
How do I change just the color of the baked map without ruining the texture using photoshop?
I searched everywhere but couldn't seem to find it.
Also, is there a way to change the texture like leather clothing? (but keeping the baked texture)

Another thing you can do it go to Image > Adjustments > Curves and give the baked texture a color--any color--then Image > Adjustments > Hue/Saturation to adjust the colors and the saturation. If you want to brighten or darken the colors I usually use Image > Adjustments > Levels. It's seems to me that Levels does a better job of maintaining the shadow contrast. Lightening a color through Hue/Saturation or Brightness/Contrast makes everything look faded.

If you want to use a specific pattern-type texture such as leather, you can add the leather texture as a new layer then change the blending mode, as gibi described. Here's a good tutorial for making your own leather texture in Photoshop.