Looking more like a boy?

Depends on the kind of look you're going for, but for the sake of argument there are essentially two 'types' of guy.

1. Fashion guys
2. Most guys

Please be aware anything I say here is going to be a MASSIVE generalisation and should be used as a basic guide not gospel

So by 'fashion guys' I mean the guys you see in magazines and on TV and stuff. The guys who were clothes that fit them well and you can tell what they are wearing is more of an 'outfit'. Things work together, effort is put in, style is involved. It's also bloody hard to pull off unless you really have the time and unless you possess the body of a god, you're not exactly looking like a 'guy' anyway.

Now when I say 'most guys' I mean these rules have applied for almost every male person I have ever met in my entire life.
What to buy:
Questions to ask yourself: Did it come from the 'mens' section? Do you like it? Is it comfortable?
Questions to avoid: Does it go with...?
Size: Bigger. If it feels a bit snug, buy the bigger one, no matter how big that is. Baggy shirts are great, and belts were invented to deal with baggy trousers.
Style: The first thing that came out of the drawer goes on you. Purple t-shirt, green combat cut-off shorts and a striped, long sleeved dress shirt? Shit yes! It covers your nakedness and that's all it's supposed to do. Maybe it looks good, maybe you try a bit, but not too hard...
Hair: "You know how spends time on their hair? Girls! You know who else? Gays!" - actual quote from a guy I knew. I realise that's not especially helpful, but seriously I've never known a guy to give a damn what his hair looks like unless it's too long or too short.
Make-up: See now this is a problem, because I don't want to tell you NOT to wear it, because you feel comfortable with it, but unless you're absolutely INCREDIBLE and able to make it so subtle it's almost un-noticeable I would have thought it would be pretty hard to wear make-up AND look/feel more like a guy...

Basically a lot of guys will go for the thing that seems most comfortable and least likely to break. Others will go for the ones they liked most that suited the 'look' they were going for.

 

For clothes I'd say look out for jeans, bootcut and straight leg jeans help to hide any curves you might have and the mens jeans are tighter around the hips so if your small they will give you a straight up and down shape and not curvy. For mens shirts and stuff if you a normally a size large you will be regular in mens or if you are a regular go for a small in men size ect.. For hair there's alot of styles you can get go get a hairstyle magazine they normally have a few pages with mens styles that you can choose from. About the makeup you could try defining your cheek, brow bones and jaw but try use very little makeup otherwise it might be noticeable and its best not to try make it look as though you have stubble or facial hair with make up I have yet to see any attempts that look convincing. And don't forget to relax and be yourself don't worry what people think of you

 

I started buy stuff from thrift stores when I started transitioning too. To find the right size, I'd just try a lot of stuff on. You can theoretically come up with sizes based on your analogous women's sizes, but it's honestly a pain in the hole. You'll find your size very quickly just trying stuff on.

As for what to buy? I'd say, if you like it, buy it. I wear a quite a few button ups, flannel because it's warm and comfortable. I prefer shirts with either plaid or ideally vertical stripes, and sometimes horizontal. Argyle is decent too if you're going fancy. I like these patterns because they mask chest curvature much much better than solid colors.

I'd have to disagree with the idea that bigger is better. (I agree with all the other stuff Ellia said though, it's very good.) If you're at all a slim sort of guy, I'd try to go for slim straight jeans. I found a couple good pair and bought them new. But only for $20 and I use them every day! I have found that Wrangler slim straight are decent and have a bit more hip room than others. My favorites would have to be Old Navy. I just find that those two brands tend to accommodate my hips/butt more, which are unavoidable bigger than most cisguys. Brands that I haven't had any success with are Aero and AE, which works out 'cause I can't afford them anyway.

For transguys, coming across as male has a lot to do with your hip to shoulder ratio. Guys tend to have narrower hips and wider shoulders. This is why I prefer slim/straight. As long as they aren't too tight (because that will have the opposite effect of coming across as masculine) I think the slim straight make the lower half of my body look smaller. If you get really loose jeans they might have the unintended effect of making us look shorter, which transguys tend not to want.

For your top (at least in winter months) it never hurts to layer. This disguises curves more and can make your shoulders look wider.

For hair.. it's hard to tell without a picture. I don't usually put a lot of effort into my hair. Sometimes I'll use paste to mess it up or get it off of my forehead. I also have a set of clippers and have been doing my own. I find that pushing my hairline back a bit just above my temples makes me look a bit more masculine. (Don't look at my profile pic, it's about a year old lol.)

I think it's possible to dress nice without looking like an outfit. Good luck, I'm sure you'll find some good things to wear!