First thing you need to consider is that: What device are you gonna draw with? (As you are asking for apps, so I assume you mean digital drawing.) Some apps work on PC only while some work the best in IOS or Android.
Some apps that are used by a lot artist: (These are some I think worth mentioning. Sorry for the not-detailed short explanation, I have never used most of them and only know that they have a good reputation.)
Paint Tool SAI (Free)
Haven’t used it. From what I know it’s good for illustration, and it’s mainly used by Japanese Manga/ Anime illustration artists.
Krita (Free)
Again haven’t used it, but I think it’s pretty popular as a free app on PC.
Clip Studio Paint (Paid)
This is the app I am currently using now. There are IOS, Mac, Window and Android version while the functions are the same on all platforms. The best part for me is that it has a huge user platform, and it provides a massive amount of assets that can be used for commercial purposes.
Adobe Illustrator (Paid)
I haven’t used it due to how pricey it is for normal learners. However, if you have a lot of savings and do not mind paying a high price, it’s probably one of the most professional tools you can find.
Procreate (Paid)
I used to use Procreate before I switched to CSP. It’s a nice drawing tool, but for me, the default brushes aren’t very suitable for the anime illustration style I am going for. I have to pay extra time/ money to find some brushes on my own.
MediBang (?, some told me that it is a paid app on pc, while from what I know it’s free on smartphones I think.)
A widely used app for artists, it’s free and a lot of it’s functions are suitable for illustrators.
ibisPaint (Free)
The vibe it gives me is similar to that of MediBang’s. Again, it’s popular for anime style beginners.
I think an important tip on improving is that, always try to get out of your own comfort zone. Most of my past time practicing, I only drew anime style headshots. This results to me that I am familiar with hairs but bad at body ratio etc. The best way to improve is that, try to draw different parts of body, different angles, different genders etc. Don’t just stick to a typical type of characters.
Another tip is that, always follow tutorials. What I love to do is that, I draw an art on my own before watching the type of tutorials. For example, I draw some sketches of hands. Then, I will watch a couple hours of hands tutorials and practice drawing hands. At the end, I will draw some hands again and compare the two of them. This process is to evaluate your improvement. Moreover, after a couple hours of practicing it’s basically a must that you will have some sort of improvement. (Maybe not much but still.) Comparing the past arts and new arts will give you a sense of accomplishment and this keeps me away from giving up.
I am not too sure about the “general shape” you are asking for. But I guess to start with the general sketch, try to look at some inspirations on social medias. Decide on a lighting, and a color palette.
My first language is not English and there are def a tons of grammar mistakes. If you want to know anything more let me know.