Playing a poker face is the basic way to act unreadable in the game poker even though you have a good card you won't show your emotions instead act as if you will lose. Just playing mind games with your opponents will make them bait your bluff. In the end if you don't want this kind hastle play online so you don't have to worry about your facial expressions.
it will not be called poker face for no reason but this term became popular because it was the basic strat use by poker players but afaik poker face is a neutral reaction , if you will act as is you loose your oponnent will think that your feeling the opposite so i dont recomend that .
You don't have to worry about your facial expressions while you play online poker, but like in "online things" there are other things you are watching for! You watch players and how they play their hands when they push big or when they are passive... you use your rise button to test others and to see their reactions (more hands you include in your observation, more accurate will be)...
What is unpredictable in poker?! When you rise all-in before the flop? After 20 folded hands? Or when you just call/fold and after some time you start raising every hand?
In my experience (and I think I have experience playing poker live & online), we play poker with our two cards (texas holdem, probably the most played poker version), and if you play long enough you will run to all sort of hands... learning how to avoid bad hands, and how to play your winning hands is not exact since, everything depends on so many things: tournament/cash, 2/4/6/8/9 players on the table, current stack, where is the dealer...You need to adjust your play by all these factors, and as your cards are different every hand, every table will be different even more!
Nobody wins all the time in gambling, there are just people with a higher winning/profit rate...
A poker face is very hard to keep up for hours and hours of playing. There are quite a few people on the table who observe any expression of your face and even look at your throat how heavily you are breathing. When playing serious for money I would recommend to wear sunglasses, a hoodie and. a scarf. This makes sure that other people can't read you that easily. Being unpredictable also helps, as long as you are playing good poker.