It kind of depends on what it is caused by. There is anti-nausea stuff you can get. There used to be, maybe stil is, stuff called emetrol. If not, there is stuff just like it, but it's called ani-nausea liquid for nausea, if you go to Rite Aid, it's the Rite Aid brand. Sorry, I feel like this answer is redundant.
During pregnancy: saltine crackers by the bed, clear liquids, rise up slowly
NO Pregnant: same as pregnant, but you could also ask your Dr about taking antihistamines, phenerghan (RX needed), antivert (Rx needed)...
The answer of flat soda (coke) is good too... (Drink slowly over crushed ice). Is about the same as coca cola syrup my parents gave me when I was a kid. This is what my mom still suggests to this day
Depends really on what is causing the nausea..