So tonight I didn't sleep very well thinking on this. Here is my little piece of advice based on my Phd experience. Take whatever you want from it:
1. PhD is not something you are very good at, it is something you survive from.
2. At some point, or very often during Phd you you consider yourself stupid, not very intelligent and you will want to smack yourself in your head from doing what you do.
3. PhD is like roller coaster but with lots of down times. Dealing with failure is what you do for a living, so get used to it! Every now and then, meaning maybe if you are blessed, once or twice a year, you might get a good result, so enjoy your little wins because there is not plenty of that.
4. Bosses are never pleased with you, there is something else you can always be doing and you're not. Not working 24/7 is a major crime, and they don't understand why you don't breath, eat and sleep science. The thing is most of the time they have already forgotten how much time does crap usually take to actually be done. And sometimes (often) they just don't care that you have a life outside lab. But the sad thing is that you actually believe them, that you are a lazy bastard and actually feel terrible about it.
5. You will hate  science, your boss, yourself, the fuckin' world... The good news are, once you finish it goes away, and you are back to your lovely self (at least I did, and yes I am lovely and I don't like you if you don't think so).
I probably could write a lot more about how shitty a Phd can be, but dear friend (yes I am talking to you) , despite whatever you are thinking right now, I believe you are a very smart person, as you should, believe too, and the good news is that you will be just fine!!