Loads of good advice here. However, as a fashion fanatic and hearing what Armin said I would suggest thinking about getting a classic cut of jean first - fashions come and fashion go, a classic striaght-leg fit will always be accepted. Personally, I have always found the traditional US companies make the best balance of high-quality denim/fit/value; Wrangler, Levi's and even Lee (I have a pair of $20 Lee jeans which fit me better and are far nicer than $500 Dior jeans which I have owned).
I always like 501's, although button fly's do take a while to break in.
If you want something 'trendier' CP company are nice, although a little pricey ($300ish). Soft, brilliantly styled and uniquely coloured, although don't expect them to last more than a year with any use (see what I said about US jeans?).
If you are talking about looking smart though, jeans are only part of what you should be looking at. If you want to be a 'proper chap' there are certain items which you need in your wardrobe, and this includes trousers! Tailor-made is best if you can afford it, there are websites which offer tailor-made suits, shirts and even jeans - just google it. Consider materials such as houndstooth, prince of wales check, high quality cottons and maybe muslin if you live somewhere hot or want something cool for the summer. And Khakis are a must along with the jeans.
You will also need to get some decent, well fitting shirts too - English makes such as Thomas Pink, Jermyn Shirts, the Savile Row Company and so on will last you a long long time but make sure you measure your collar. Nothing like an overlarge collar and poor fit on a shirt to look awful. I like tab collars myself, but then I like wearing ties. Of course, next you will need some jackets - I like a nice boater, but any blazer really, a nice Harris Tweed is always acceptable for bad weather if you can afford it... jumpers - Scottish Arans are timeless, comfy and very warm but you will also need plain cashmere or pure wool ones, a smart cardigan, especially if you can find one with suede panels on, turtlenecks are nice too...
Then there are the accessories - its no use you dressed up to the nines and then pulling out a nylon and velcro wallet is it, Sir?! So you will need to budget about $200 for a nice wallet. I particularly like prada wallets myself, but any kid leather one will do.
And then there are shoes... don't even get me started here! If you look at your wardobe and only see trainers.... then you are a very bad man! Not that trainers are bad per-se (I love trainers) - I like to wear a boxfresh pair with a suit sometimes - but every man needs a fine pair of brogues or chelsea boots. Loafers are a must too and I always like to have a desert boot. Remember you will need black and brown pairs too depending on whether you are wearing jeans or smart stuff.
Then on to coats - a nice crombie or raincoat is a must. Aquascutum/Burberry do some lovely lightweight raincoats for about $700.
Dont forget belts, cufflinks and a nice pen too (Montblanc, Cross)... oh, and don't forget the watch of course!
Try searching google for 'essential men's wardrobe' I am sure you will find plenty about it.
I absolutely guarantee to you that if you start taking care over what you wear and look like you will feel so much more confident in yourself. Women will also look at your differently. Finally, you will also become addicted to buying classy gear too! Mmm.... shoes...
Good luck!
Robsa