A great academic who taught me once said of a PhD (paraphrasing); "It's not going to be your best work and it'll not be amazing. It's just your trade union card. Nobody gets really good at research until they're 10 years in."
Pragmatic advice. The problem you solve doesn't have to be paradigm-shifting or world-changing, just a bit above what humanity already knows [1].
w.r.t your question; pick an advisor you know you can work with for $x years first. Read papers before you pick your topic and keep looking for "holes" - these are where you can make your little dent.
Comments
A great academic who taught me once said of a PhD (paraphrasing); "It's not going to be your best work and it'll not be amazing. It's just your trade union card. Nobody gets really good at research until they're 10 years in."
Pragmatic advice. The problem you solve doesn't have to be paradigm-shifting or world-changing, just a bit above what humanity already knows [1].
w.r.t your question; pick an advisor you know you can work with for $x years first. Read papers before you pick your topic and keep looking for "holes" - these are where you can make your little dent.
[1] : http://matt.might.net/articles/phd-school-in-pictures/