This first recommendation is Ibispaint. Ibispaint is a drawing program made for the purpose of creating webcomics or illustrations. On the Google Play Store, you can download Ibispaint, the original version for $8.00, or the newer version IbispaintX, a free version with just as much quality as the paid one. These are great, and if you are looking for a cheap or free high quality app to use, I recommend this one.

This is ClipstudioPaint. Clipstudiopaint is a drawing program used by professionals. It is made for artists to make mostly webcomics and or manga, but you can still make illustrations. Even though it is $54.00 or around that for a year, it's wide variety of brushes and tools make it worth the pay. If you are really invested in drawing professionally, this is an amazing app.

This last recommendation is Krita, a free program to use to draw. It has may features that a professional app has, except some of the shortcuts, such as the double tap to undo and the triple tap to redo. It has a wide variety of features and brushes to use, and it It is a great program for those who aren't to sure if they are ready to invest in a program.