A great deal could be said on this topic. Here are a few thoughts that may be helpful. Test them against your own experience. First some general points, then to your specific questions.
1) Make good use of the morning, which is an excellent time for such activities as reading, writing, study, and meditation. But to put the morning to good use, one must arise early. I get up at 1:30, but you needn't be so monkish. Try arising one or two hours earlier than you presently do. That will provide you with a block of quiet time. Fruitful mornings are of course impossible if one's evenings are spent dissipating. You won't be able to spend the early morning thinking and trancing if you spent the night before drinking and dancing. The quality of the morning is directly affected by the quality of the previous evening.
2) Abstain from all mass media dreck in the early morning. Read no newspapers. "Read not The Times, read the eternities." (Thoreau) No electronics. No computer use, telephony, TV, e-mail, etc. Just as you wouldn't pollute your body with whisky and cigarettes upon arising, so too you ought not pollute your pristine morning mind with the irritant dust of useless facts, the palaver of groundless opinions, and every manner of distraction. There is time for that stuff later in the day if you must have it. (And it is a good idea to keep an eye on the passing scene.) The mornings should be kept free and clear for study that promises long-term profit.
3) Although desultory reading is enjoyable, it is best to have a plan. Pick one or a small number of topics that strike you as interesting and important and focus on them. I distinguish between bed reading and desk reading. Such lighter reading as biography and history can be done in bed, but hard-core materials require a desk and such other accessories as pens of various colors for different sorts of annotations and underlinings, notebooks, a cup of coffee, a fine cigar . . . .
4) If you read books of lasting value, you ought to study what you read, and if you study, you ought to take notes. And if you take notes, you owe it to yourself to assemble them into some sort of coherent commentary. What is the point of studious reading if not to evaluate critically what you read, assimilating the good while rejecting the bad?
The forming of the mind is the name of the game. This won't occur from passive reading, but only by an active engagement with the material. The best way to do this is by writing up your own take on it. Here is where blogging can be useful. Since blog posts are made public, your self-respect will give you an incentive to work at saying something intelligent.
5) You say that you forget what you read.
Well, there is little point in learning something that you will forget. The partial cure for this is to read in an active way, with pen in hand. I use pens of different colors for underlining and note-taking. Write key words on the top of the page. Isolate and mark the key passages. Make a glossary on the book's fly leaves. When a book arrives, I note the date of its arrival so that I an track my intellectual biography. At the end of a chapter I note the time and date of my first and subsequent readings of it. Reconstruct the author's arguments in a notebook in your own words. Look up reviews online, print them out, then insert them into the book. A properly annotated book is easy to review, and of course review is essential. Review fixes the material in your mind.
You ask how many books or articles should one read in a day.
I'll use myself as an example. Yesterday, N. Rescher's Aporetics arrived. I read and annotated the first chapter this morning slowly and carefully. Then I sketched a blog post in my handwritten journal that was inspired by Rescher's chapter. Then I went back to Palle Yourgrau's Death and Nonexistence which I am working through and mulled over a few pages of that. These activities took me from 2:00 am to 3:35. Then 45 minutes of formal meditation. Then I logged on and put up a couple or three Facebook posts. Around 5:20 I was out the door for an hour on the mountain bike. The main thing is to read and write every single day.
You ask whether one should start by reading the ancients or by studying current debates.
You could do either, as long as you do the other. You need to have some issue, problem, or question that you need to get clear about. Perhaps you want to understand knowledge in its relation to truth, belief, and justification. Contemporary sources will give you some idea of the relevant questions. Armed with these, you can profitably read Plato's Theaetetus.
You ask whether you need a mentor.
No, but it helps to find one or more intelligent individuals with whom you can interact productively. But even this is not necessary, and in any case, these individuals may be hard to find. To exaggerate somewhat, all real learning is via autodidacticism.
