I am also a complete newbie to this like you working on my first army.
The best advice is to watch as many YouTubes as you can about painting miniatures.
There are two channels I watch and they both have AMAZING painting tutorials. I've learned so much watching them and am practicing a lot on sprues before committing to the models.
Check out: WarhammerTV (Duncan does amazing painting tutorials) and also The Apathetic Fish's channel. You can literally learn every technique you will ever need watching those vids. They are incredible.
https://www.youtube.com/user/GamesWorkshopWNT
https://www.youtube.com/user/Alanduin1
Things like shading, and using lighter colored layering paint with edge highlighting make huge differences with making the model pop.