If you go for a thumb ring, and want to get another ring wear it on your ring finger or middle finger on the opposite hand, just dont go overboard and get fuckloads unless your gonna go down the rocker route and load up every part of your body with them.
Hardest advice I can give to you is endeavour to choose non cliché or generic items that everyone else has something like - trust me thats farking hard to do.
Personally I usually got for combos of contrasting jewelry, for example Im wearing as I type this:
A classic 1940's style gold watch with a black leather strap with a very thin surfer style beads and leather bracelet on my left arm I picked up in the Pyrenees Mountains in the south of France. And that Titanium and steel wire thumb ring I picked up in a poker game near Marseilles.
On my right hand im not actually wearing any rings (although as a man id suggest signets types are pretty good choices if you do want more) but I am wearing a 2m thick leather band thats about 2 foot long thats been wrapped my hand with a carved 1inch long very thin bamboo trinket that I picked up while building wells in Thailand and next to it is a gold Byzantine style chainmail chain I got off ebay (lol no story there)
Thats an example I have a few pieces I chop and change but I like this combo because it blends well with different clothing styles, worst thing you can do is get a certain style of clothes and different style of jewelry which are not congruent! this Is why I switched to using gold and silver since the 'only silver' style was limiting and can give off a cheap vibe sometimes
My next purchase is some custom made gold cufflinks with my family crest on it, although im gonna hold off to xmas to buy them as I went to get pairs for my father and two brothers at the same time since I know they will love em and I can get a discount then
Just have fun with what you get and when you wear it dont pay attention to them, think of them as simply part of your body which will assist in them being natural.