. . .
First you will need to distinguish a light source and add highlights accordingly.
I find it really helpful choosing a light version of the colour of whatever light source used.
You will need to structure the glow layers like this:
This structure will be beneficial towards you. An easy way to make glow is using the effects section of IbisPaintx.
However you may also like to draw them on. If you do this use a faded brush which will create a gander out effect
You need to blend the edges of the glow used out to create a more smooth appearance.
These are just a few things to look out for, sorry it's not very detailed xx