Here's a piece of advice I haven't seen mentioned on this topic: people are typically irrational about sex, and you can make yourself an appealing partner to a minority of people who aren't being "well served" by the general population simply by being extra open-minded. In short, I'm going to advocate exploring kink spaces.
First, cultivate the aliefs that there is zero shame associated with consensual sexual activity of any kind, and that there is no space for sex-specific morality in your code of ethics. The slogan "everyone owns exactly one body" is a good start.
If you've got this in your head, hopefully you'll want to do just about anything your partner wants you to. The attitude to cultivate is to be "good, giving and game".
Once you've got the mind-set right and done back-ground reading, you can start looking for kink meet-ups and groups in your area. The really nice thing for you is that kinksters are basically sex nerds: everything is talked about explicitly, negotiated, scheduled, double-checked, etc. There's worlds of hand-holding at every step.
I could be just plain wrong about this, but my belief is that sexual tastes can be "acquired" in the way you can learn to like strong cheeses, silent films, whatever. So have a go at acquiring this taste --- because I think it'd prove useful.
I also think that people who hang out in kink spaces are more likely to have non mainstream sexual tastes. You are, I would think, more likely to find women who are really keen on fat guys (these women do exist) in these spaces. It's been my experience that in kinky and similar communities (e.g. the poly community) people (both men and women) who are not conventionally attractive are more likely to be sexually successful than they would be outside these communities.
I want to spend a substantial fraction of my time optimizing myself in the direction of being more attractive to females, and I'd really appreciate your suggestions on how to do so.
Why
It should be pretty self-explanatory, but in case you're wondering: relationships are a big part of personal happiness, and where I am now, I feel more inclined toward increasing the number and variability of short- or middle-term sexual relationships rather than just picking a girl who wants to be my wife and run with it. But at the moment women aren't exactly chasing me down the streets, so I want to offer them a more pleasant experience of my company than what it already is.
Mind-killing
I sincerely think this post should provoke none of the above. I'm not asking for ways to trick women into liking me, nor about gender differences about what males prefer over females, etc. Please try really hard to avoid mind-killing subjects into your comments. I'm 'just' asking for ways to change myself into being a more sexually attractive human being.
Caveat(s)
I'm aware of the dichotomy lying around: attraction can be created vs attraction can only be amplified. In both cases there should be at least something that can be done.
I'm also aware that some people strongly dislike posts full of personal details, so I will try to keep them at minimum, while at the same time trying to provide the necessary description of my situation.
I would like
Try to aim for advice on stable improvements, about aspects that are proven to be sexually attractive to straight females, in the age range of 20 to 40.
For example, I know that height or facial symmetry are proven to result universally attractive, but I cannot really change that, and sole-lifts or make-up are so short-term solutions to border on 'tricking women' (yes, I know that women use those tricks too, I simply would like to invest my time better).
My situation
This is the shortest possible description: I'm a straight male in my thirties, heavily overweight, living in Italy in a 20k people town, with a job paying me about $20k a year.
If you think you need more details ask for them in the comments or PM me.
What I'm already doing/planning to do
The first obvious choice is getting fit, although it's about two years I'm trying different diets with no results, so I'd really need pointers in that direction. I've also heard about training programs that tells you to concentrate on shoulders, because apparently shoulder-to-waist ratio of 1.5 or more is especially attractive.
I've also been told multiple times by multiple sources that women values confidence, competence and leadership. I understand the confidence part in being able to express without embarassment your interest (but still in a socially graceful manner), but I would really like pointers about what area of my life I could engage to become more competent or a leader. In what domains women like competence/leadership?
My only hobby at the moment are the game of Go and dabbing in math/logics/AI, which, as fascinating as they are, are seldom considered very attractive.
What I'm not sure about
Is fashion important? I understand that I need to dress well for my built, but I would like to know if a Versace button down shirt is more attractive than a plain brand one.
False beliefs
Do you think am I doing the right thing? Or am I wrong in my search for attractiveness? Should I concentrate on something totally unrelated? Dose the physical aspect matter or I should concentrate more on character? Am I completely off track?
If you think I'm grossly mistaken, in the name of Omega let me know!
Downvote
If you think this post doesn't belong in a community devoted rationality and self-improvement, feel free to downvote, but at least try to indicate a way to better phrase the problem or point me to another community I can ask the same question.
Thank you very much!