What is a strategy to do theoretical research? Thanks to some great SE answers on a previous question I posted, I realized that even though I don't have an RA at the moment (I am a first year PhD student), I must start my research ASAP. I am convinced that this is great advice and want to follow it. 

But the concept of 'doing research' is still not perfectly clear to me. I am interested in convex optimization, that's what I intend to do my PhD in. So as of now, for my thesis, I have this vague idea in my mind that I'd solve a problem by maybe coming up with a cool algorithm and give some nice proofs using convex analysis. 

But exactly how to start is a mystery. Here's what I think I should do: read a paper that looks interesting to me (this could be because of the abstract, or maybe it's a paper that has suddenly got very popular, or it could simply be based on the author's reputation, etc), thoroughly understand their results by working out proofs of all their statements, and then try to see what happens in slightly different cases than what they mention. Maybe relax some assumptions they make; or go the other direction, add a constraint and see if the algorithm can be improved because of this constraint, etc. 

Is this how it's done? I feel so lost right now. When I try doing this, I have so far (in six months) not been able to really think of anything new. Even the existing proofs that I get are so complex, I can't think of any way to come up with something new. Can someone please give me some tips on how one gets started in theoretical research - how to come up with a problem, and how to proceed from there? 

EDIT_ Adding more information: I don't have an adviser yet, and this is the post I am referring to in the first paragraph.
In mathematics, a paper with 20 pages of proofs does not have twenty pages of original ideas. It might have a page worth, maybe. The rest are combinations of 2-6 previously known ideas, often with little or no acknowledgements of their first appearance [footnote 1]. 

To beginning graduate students, I strongly suggest to read much older papers. They are usually much shorter, much simpler, and actually allow to learn ideas in their simplest. In my branch of mathematics, that means papers that are at least 30 years old. General useful mathematical background papers go at least 60-100 years.

A good way of doing research is just to be curious --- after all this is what got you into the position you are now, right? Whenever you are curious about something, try figuring it out, look for some way of doing it, search references, read whatever looks interesting, swear at whatever does not. Keep journal with your questions, observations, dead-ends, ideas and swearing. Occasionally, when there is something particularly nice, add those 5, 10 or 15 pages of formal expository and technical scaffolding that is needed to convey your message to others [footnote 2] and share with the world. That is research.

[1] Many find it embarrassing, awkward and out-of-place to write ".... by Cauchy-Schwarz inequality. (This way of applying Cauchy-Schwarz inequality I learned from [ref] which is completely unrelated to the current topic). Next we can bound (5) by..."

[2] After spending much time thinking about X, you will find that you need to spend much time to explain the basics of X to anyone who has not spent the same time thinking about X. That is why you need all that scaffolding.