Lets

 Get going.
I always do a light pencil drawing first.
If the drawing is wrong then the painting will be!
Don't be afraid of using a ruler it will help you get the proportions. Eye level, , distance apart, widths of head.
If I am painting something new I use a print and the computer image.
Using a ruler allows you increase the size but I would go much above paper size 10×12 inch canvas paper.

 Don't blow the family budget! I use pound shops. And The Works for my Canvas paper books and water colour. I spend a bit more on acrylics because low price one's are watery and don't behave on the brush or canvas.

Trim a brush down to a short fine hair.

Do a wash light colours first 

 Darker colours come later

 Eyes

 Eyes aren't flat they are a globe so creating that is a challenge on flat paper

 Do the drawing. Spend time learning about the eye of the subject.
The retina of a dog are brown.

 The angle of the light will create the curve effect.