A good guide how to use AI ?

I have no issue with using the generative fill.   It sounds to me as if you are using just the rectangular selection box.    You can use any number of selection options to follow the curves of a road for example.    

Now you just cant type "skid marks" for the prompt: Adobe thinks you are talking about underwear skid marks and wont allow it.










I had to change the layer opacity on this a bit- but it's hard to tell that the tire marks are not part of the original image.


You asked about a guide:  follow the AI links:

It's still useful to know how we did things before Ai and Generative Fill became a thing.

One idea is to use a brush preset.

Set spacing so each stamp of the brush aligns with the last

Set Angle Jitter to Direction so the brush orintates to the direction of the brush stroke, and to keep it nice, Stroke a work path.  You'll need to mask out the start of the stroke to make it tidy.

This not going to work so well with curved lines, because there will be gaps on the outside of the curve, and obvious overlap on the inside, so best to make them straight, and use Free Transform warp to do the curve.

Now we need to give it some perspective, which we do with Fade (make each stamp of the brush smaller than the last.

Because our spacing is so large, we need very low value for Fade.

We are now left with two problems. 1) there is an obvious step with each new stamp, and 2) the stroke has gaps toward its smaller end.  Remember, the overlap shows if made too big.

For the first we need a new preset with some perspective.

For the second, we have to compromise on spacing, and make the stroke longer than we need, and mask off the excess. That gets us to here.

Place on your road.  Free Transform > Warp > Flag or whatever suits.

Set to Multiply and reduce opacity.

Grop the two layers and use a layer mask to align the ends.

I have used the same method with brush presets to create rope, chain, bike chain presets.  They all work well, but will not go through tight curves because of the gaps, so try to keep the strokes straight, and FT > Warp to fit the scene.

All of the things you mentioned are ways to explore to get the wanted result. A good prompt is the key to a good result. Firefly and other generative AI models are just new tools and they only can get you a result based on their training data. That is why more often than not we as designers and illustrators need the skills to work with various tools inside of Photoshop to composite certain elements together to get the desired result. This might also include to look for (in your case) tire skids on Adobe Stock or other sources and apply it to your image through different techniques like using masks, distortion meshes or other techniques. There is no one tool fits all purposes. That is also – in my opinion – the fun thing of working with creative apps like Photoshop. There is always so much to explore and learn. So maybe in your case try to get a really good stock image of tire skids, extract them and apply them to your image with different image manipulation techniques as opposed to use Firefly to generate it.