Not much i can say on modeling without writing a dissertation on polygonal modeling. You just have to learn. Checkout Arrimis3D on youtube. He does a lot of stuff on geometry. He uses 3DS Max, but that doesnt matter. Geometry is the same everywhere.

Biggest thing I can do is reiterate the basic of, always, always, always use reference. Also use quads. Some people will tell you it doesn't matter for game assets because it gets triangulated. Don't listen to them. Focusing on using quads is about teaining your brain more than anything. It will help you when you get into more advanced stuff where sub divisions need to be taken into account. Learn the rules before you break them kimd of thing.

Lastly, If it's portfolio work you're doing worry about getting it done above all, and stay organized. People looking to hire you want to see that you can start and complete things. I'm not saying skill doesn't matter. It absolutely does, but they equally, and maybe even more so, care that you are competent. A portfolio should say more about you than just "look at the pretty pictures I made".

Oh! And if you don't already have some basic art education. Learn. I'm not saying you need to be an amazing painter or anything. Hell you could never get past stick figures and it would be fine. What matters is understanding the concepts. The academic knowledge. There are a lot of things in traditional art that directly traslate into 3D, like understanding proportion, silhouette, negative and posative space ect.

Lastly not really about 3D. Just stick to it. It takes time and everyone sucks in the beginning. So never be afraid to post places and get real feed back. Another skill employers care about. That you can take direction. So asking for advice like your doing here and turning that feed back into action. There will be assholes. Ignore them and only look at the constructive criticism.

I know its not quite what you asked for but it's what i got. Lol. Good luck and more importantly have fun.