how can i improve

[mental idol]

all help appreciated!

[autumn rampart]

All I can say is practice more and get some darker lead

Or press harder

Your contrast is really low which makes it hard to see the details

[fresh elm]

I'd say maybe the shading need to be more specific I mean if you look closer and look at the dark shade on the 2nd picture compare to the lighter one need to be more like this. this picture is more detail and more specific unlike the shade, you get me?

Like here's a example of shading but just in black and white you can see where the darks part and light

For the light part don't hold the pencil firmly use it lightly and slowly make your way

But the rest of the drawing you did is good

Focus more on shading

[vernal latch]

In addition to what others have already said your drawing is a lot wider and shorter than what the reference shows. You also aren’t paying attention to the gesture of the body. Yours looks more stiff while the ref is bending over a lot more