In these days and age, miserably few would consider pursuing a Ph.D. degree in science. In case some are still pondering about it, read this article first before pushing head on into it. This is my only advice for now.
What’s it like to get a Ph.D. Degree in science?
(If the above link does not work, use it for copy-and-paste in search engine.)

After perusing the pros and cons outlined by the author of the article, let me know if you have more questions.

At any rate, enjoy a good read.