A few things I'd add here from extensive personal experience since my teen years.
Firstly, according to my doctor and all the research I did on the Net when I was a bit younger, the sleeping on the back thing , and the diet thing are not truly factors. Those are more like what they call "old wives' tales" about acne. The reason greasy foods/snacks were originally associated w/acne breakouts was simply because many times people snack on stuff like that and then do not wash their hands prior to touching their face , or going to bed. Going to bed w/hair product in your hair is not that good of an idea. This is the reason alot of girls will get pimples , zits, which they can more easily conceal w/makeup and their longer hair, etc. But they get it because they come home so frequently on weekends and stuff, head full of gel and spray, and just do a basic wash-up and go to bed. That junk gets on your pillow and you wallow around in it, rubbing your face on the pillowcase all night, etc., and you will get a breakout going eventually. Wash your hair before bed when practical. Change pillowcases at least once a week. Wash the others and replace.
Secondly, the oil factor. Lots of guys get "greasy" during the day. Depending on different factors, genetics, and believe it or not ethnicity. Myself , being Italian, I had in high school REALLY bad skin as far as greasiness goes. Basically, the same as the type you see amongst alot of Latino people. Thus the old stereotypical nickname "greaseball".
The good news is nowadays you can fight that a hell of a lot more effectively than I was able to in my h.s. years. Back then we only had those OXY or Clearasil or Stridex pads towipe all over our faces and de-grease them. Sure those will de-grease you, very temporarily. Problem w/those is they contain salicylic acid , and that overly dries your skin out , and thus w/in about an hour and a half or so , if that, of application, you are once again looking like a "greaseball" , and even worse this time probably. And the more you keep slapping that OXY on, the worse it gets eventually. I would save the OXY pads, and any other pad like it, for treating solo zits, and apply only to the zit and only at night before bed. For the daily grease, purchase either Biore "cleansing cloths" (the ones WITHOUT the salicylic acid ; it specifies on the boxes which is which) and/or Biore "mens' blotting papers". Both are great for a refresher before going out , or whatever, if you're not in a position to actually shower. For serious zits, try a product called Zapzyt, w/which I've had enormous success (overnight success really). NEVER mess with a zit that does not have some kind of visible "white" head on it. You will make more of a mess out of it than it's worth , and leave a scar sometimes. When you do have one that looks like it's ready to be destroyed, do so, and then put hydrogen peroxide on it. That's a disinfectant and speeds healing. For blackheads, do not squeeze your skin to try to get them out, or if you have to do so very carefully and minimally. You can badly abrade and damage the skin when you do this. The top layer breaks easier than you think. Use for this, again a Biore product (and no I'm not a Biore sales rep) , deep pore cleansing "strips". They'll be located right by the cleansing cloths at your local store. Pulls those blackheads right out for you. As far as a soap, and frequency of usage, for those of you w/oily skin I would recommend (guess which brand) , yes Biore, "shine control" oil-free facial wash. For guys w/non-oily skin , just go with some kind of good brand name facial wash (Biore, Neutrogena). Don't use hand soap or any other type of body wash on your face. For the older guys here, unless you have really really bad acne for whatever reason or are going through a breakout cycle, one good face-washing a day w/this stuff will be very effective. Washing twice a day is more for younger guys , say under 25 or so, who are more prone to the occasional hormonal irregularities, testosterone "spikes" , etc., which help produce the breakouts. You'll notice when you only wash once a day that you produce far less oil during the day. For shaving, try Edge shaving gel for sensitive skin. It actually seems to me to clear up existing pimples when I use it. To help avoid ingrowing hairs, which can also produce post-shaving breakouts, make the pores of your face open first by using a hot cloth. Yes, hot. (That also makes the stubble come off easiest). Then after the shave you use a cold cloth to close the pores up again. If you use any aftershave, alcohol-free is best; less "sticky", doesn't "burn", and plus alcohol also overdries the skin, thus leading to more of that oil production again. If you shave at night before bed, using a little lotion ( make sure it's NON-comedogenic; that is, NOT pore clogging) like Curel for instance, is good as an "aftershave". When you shave it does dry the skin out a bit more than usual, that's why lotion is good for an aftershave. But like I said, I would only use lotion on the face before bed, because some lotions leave you feeling a little too "heavy" or greasy. In general avoid touching the face, running hands over your face, etc etc, if at all possible. It's really best not to. Your hands pick up a lot of potentially pore-clogging oils and dirt particles over the course of a day. Best to just keep them off of your face if you're at all prone to breakouts. Doing things like wearing a baseball cap for a long time and then flipping it around and putting it on backward is also a bad move for the acne-prone. The inside of that cap is resting in the back of your oily (possibly product-laden) hair , and then you flip it around and put it to your forehead. You know what I'm saying? So basically just use some common sense when dealing w/things like that, in my opinion. Good luck.
One last thing, a UV lamp or sunbath , better known here as "tanning beds" , is a good thing to do maybe once a week if you can. DEFINITELY helps prevent acne breakouts when used like that. In fact, dermatologists used to give people w/severe acne UV light treatment as part of their cure. So it's known to help. Avoid "spray tanners" or any kinds of fake do it yourself tanners. Not only do they (usually) look somewhat fake , but those things clog the pores and, you guessed it, will lead to a few pimples sometimes.