I recently have been settling on a method which seems rather reliable.
Using this method, which is mix of the writing of various traditional & modern authors, I approach the chart in such a manner:

1.) Understanding which planet in the chart afflicts the querent. Whether it'll be L6, L1, the dispositor of L1, the Sun if L1 is combust or a planet in a disharmonious aspect to L1. May also be a planet on the ASC or within the 1st house.
This is a science all to itself, but I won't go in depth here.
2.) Afterwards, I've settled on the following method.
~ to use houses as areas of the body (say 6th is intestines, lower belly, etc.)
~ to use signs as the way the area of the body is functioning (say a fire sign may show inflammation, a water sign coldness and excess of phlegm, Libra may show an imbalance, etc).
~ to use a planet as the human function or the bodily mechanism, by which the problem is caused (say mars may be a cut, the sun may show a burn, venus excess of some hedonistic activity, etc.).
3.) combining the above, in order to create a coherent picture, which blends well with what the querent is describing.

What do you think?
What are your method/s for diagnosis?

Hello DimaGur,

Your approach is coherent and it is true that houses = signs in medical astrology.

To quote Kira Sutherland, the Sun is organic, the Moon functional and the AS physical.

I also include midpoints and Uranian planets in diagnosis and Solar Arcs + Transits to show up current condition. And an activation of a natal placement is foremost.
Besides the traditional ailments associated with planets, here is a resume of Trans-neptunians as investigated by Eileen Nauman in 'The American Book of Nutrition and Medical Astrology'.

Cupido
childbirth and oftentimes a family member being sick
Hades
Similar to Saturn but more serious, leaving you with nothing.
Kronos
A good indicator of recovery because of a surgeon's skill
Apollon
Complications or misdiagnosis. Indicates more of something.
Admetos
A seed that sows illness. Starting small. Suffocation, choking, Connected to the mother.
Coma.
Vulcanus
Like a volcano. Eruptions. More of the planet it connects to. But tremenduous reserve of energy.
Poseidon
A guardian angel. Diseases on mental side or orphan diseases.

And I always look at 3 specific midpoints
Mars/Saturn = accidents and stopped activity which oftentimes comes with an illness.
Saturn/Neptune = chronic illness
Mars/Uranus = accidents, operations.

A double transit is always significant. For example, Saturn aspecting Neptune and Neptune aspecting Saturn, look at the midpoint Saturn/Neptune in the chart. See if it connects to personal points Sun, Moon, AS or MC.

In general, diseases can be viewed as expanding (Jupiter) or contracting (Saturn). With this in mind, a transit of Jupiter can be deadly if for example the lungs are filled with water.

Best to you,
Ouranos

Ouranos,
Thanks for the additions.
Some good points in there!