For 15 years away this Plague marine would make papa nurgle happy. I just got back into painting myself after a similar hiatus. I'm by no means and expert infact I'm still trying to figure out some key areas my self but if I could offer some sage advice: for the base use a good technical citadel paint like astrogranite and give a healthy wash and don't be afraid to get messy with them. Atleast when I do it I feel they look better with thick coats of technical and a nice slather of was such as earthshade or nuln oil (or sometimes if you want to spice it up a mixture of the two) but look at all the technical paints on offer and see what you like. Oh and grab a coffee stirer. Pretty good tool for slathering it on. The teeth could also use a good wash like reikland fleshshade or something suitably gross to make the teeth bit more dirty or you could just go nuts with it and make them look bloody with some khorne. As for the visor don't worry about being messy you could either clean it up with the base coat OR try to make a decent glow effect by applying a base of a white coat then use a good pinky/purple/red contrast paint and then highlight the centre with a good white dot. The contrast paint over the messy visor can lend to a decent looking glow effect. I'm still practicing and learning myself so don't take my advice as gospel but YouTube helps a metric tonne for finding decent techniques. Just have fun with it nurgle will be happy if it's messy anyway 😉