I've always doodled on notebooks and sketched on corners of paper.
Over time I've gradually found my illustration style and now I am able to include this with my books. On the first page to every book, I will include a personalised illustration, whether that's something you have or something I find to illustrate from your photos as reference.
Here are a few examples of my illustrations below.
This book was illustrated and designed for the lovely Lloyed and Yaya from HandLuggageOnly
Click the link to check out their blog post review on Ella's Books and their trips of 2018.