If sight reading is important to you there must be studies on it.
There has been done quite a lot of research in the field of sight-reading. I don't know what I am allowed to give links to, but a general summary will lead anyone interested in the matter to find what they need to improve in themselves.
Provided the "subject" is able to read notes and has a reasonable knowledge of the keyboard topography (through scales, formulas, idioms, etc.), one may conclude the following (in random order):
1) sight-reading without auditory feedback leads to only slightly more mistakes than normal feedback;
2) omitting visual access to the keys completely results in markedly poorer performance. For good planning one needs to look at the keys sometimes;
3) working memory (the ability to store info in the short term memory to work with it) is paramount;
4) preview of two beats leads to a slower tempo, larger variability in note durations, and errors. Subjects performed better with previews between two and four beats or, ideally, with previews to the end of the next bar. Training preview (and probably also working memory) away from the instrument seems to be the logical approach if one wants to develop the skill quickly, the more so because pianists and organists have to zigzag through several staffs;
5) quality of interpretation (not merely pressing the right keys, but communicate something): we form meaningful units that are influenced by our previous knowledge and expectations. The better we are acquainted with the style and idiom of the piece, the better the results will be;
6) One can never sight-read beyond the level of rehearsed performance, which is an understatement, of course;
7) Training helps, but one has to pinpoint the real problems, which may be different with different subjects.
Paul