if you want to invest in bitcoin, don't look at the value just invest, don't be fooled by the market swigs, there are only two things to do with bitcoin now that is buying and holding
keep buying no matter what the price it, and hold the rest, if you want to make more bitcoin from the one that you are hold, invest them in some other things like altcoin that have a great potential or mining
actually i never bought a single bitcoin, i like to generate them via mining, it's more anonymous for me, and more profitable, even if it's slower
But if you want to invest your bitcoin make sure that its trusted so that you"ll now regret in the end. Because nowadays there are many scammers. For me the perfect time to invest is when you know that your bitcoin will be double or even you are sure that it will grow.