If you know a good and safe place to invest(studying carefully before investing  your Bitcoins or a part of your Bitcoins if it is a serious company,for how long is active ,it is paying his members regularly etc.)you can invest.You can do some trading,selling at high price and buying at law price,but there are some risks involved ,you have to know and trust the persons you are trading with.Anyway I think is safer to keep at least 80% of your Bitcoins in your wallet,because it is the safest place:), and in the future you can sell your Bitcoins ,when his price will be multiplied.