A lot of piano students have a hard time with time signature 3/4, 3/8, and 6/8. Three is not easy to feel for most humans because we have 2 legs and 2 arms and walk with 2 feet like, 1-2-1-2. Almost everything in our everyday life is surrounded by 2, not of 3. 99.9% of the times, even tables have 4 corners, not 3 corners. A table is nothing to do with music. But my point is that it's hard to feel three. You probably noticed if you are playing a song in 4/4 and right after that if you are to play a song in 3/4 you notice it's hard to do because it's not easy to shift the gear. So, how should we do this? You have to feel it inside your body. Don't just count 1-2-3 and expect that you are going to feel three. So, I have a suggestion. Stand up and actually dance 3/4 or waltz. Down - Up - Up - Down - Up - Up, or Boom - chat - chat - Boom - chat - chat. You may say, "Excuse me ?! No ! I'm not gonna do that !" Yes, you may look silly doing that. But it works because you have to feel the 3/4 time inside the body. Once you shifted the gear to 3/4, you are in 3/4 groove solid ! Then, also, once you actually practice shifting the gear back and forth many times between 4/4 time and 3/4 time, you'll be able to shift the gear instantly in the future. It's about the "groove", not really about counting or mentally think about 3/4 time signature.