Shading cylinder and tree

I am new to drawing, sketching and pencil shading. I have been working on pencil shading of late. By varying the tones or by applying correct light tones, mid tones and dark tones gives the feel of depth and 3D effect. I still don't get that exactly. However these are some things I tried lately.

Shading a cylinder

Shading a cylinder

Shading basic shapes

Shading a tree

Ref videos:

Shading a sphere and cylinder

I was practicing pencil shading from last couple of months. There are many useful tutorials with tips on youtube as to which pencils to use, how much pressure to apply etc. Looking at the tutorials, I shaded several times but wouldn't arrive at a decent shaded sphere. After many trials I came up with "hmmm not so bad" kind of a shading (at least for me). This tutorial was very helpful in getting a "hmmm not so bad" shading of a sphere. 

I used 2H, 2B and 3B pencils.

Reference video: 

Reference video:

Pencil Drawing 38 - Tom and Jerry

Image Source : Google

Pencil Drawing 37

Image Source : disneyclips.com

Pencil Drawing 36

Image Source : Girl1 and Girl2

Image Source : https://www.pinterest.com/pin/70650287890214598/

Image Source : https://www.pinterest.com/pin/442478732130178632/

Image Source : https://www.pinterest.com/pin/394416879867222770/

Pencil Drawing 35 - Disney Pilots

Image Source : Google Images, Link1 and Link

Pencil Drawing 34 - Aladdin

Image Source : google images, pinterest etc.

Pencil Drawing 33 - Calvin and Hobbes

Image Source : Google images from Calvin and Hobbes comic strip 

Pencil Drawing 32 - Alice in Wonderland

Image Source : Google images

Image Source : www.disneyclips.com

Image Source : www.disneyclips.com

Image Source : www.disneyclips.com

Image Source : www.disneyclips.com

Image Source : www.disneyclips.com

Image Source : www.disneyclips.com

Image Source : www.disneyclips.com

Image Source : www.disneyclips.com

Image Source : www.disneyclips.com

Quotes are from Alice in Wonderland.

Pencil Drawing 31

Image Source : https://www.pinterest.com/pin/838232549375618265

Image Source : https://www.pinterest.com/pin/523825000408797972/

Image Source : https://www.pinterest.com/pin/838232549375618092/

Pencil Drawing 30 - Snow White

Image Source : https://www.pinterest.at/pin/417849671675837468/

Image Source : https://images.app.goo.gl/FYkiGguiarup8UEG9

Image Source : https://images.app.goo.gl/mVahvHCfH1JeRwhGA

Image Source : www.disneyclips.com