Advice for a photography beginner?

I'm starting to pursue photography as a serious hobby (and hopefully along the line a career), so basically my question is for the more experienced photographers. My question; What do you wish people would have told you when you first started? Any general advice? I just want to be prepared.
The equipment i'm working with is a Nikon D90; lens 18-105. I'll be getting more soon, but I'm not too educated in the whole mm thing yet, and I've just learned what aperture means.

Added (1). Okay, I meant that I'm just beginning in DSLR. I've read many guides and such, but I'm just looking for some direct advice.

Nikon D5000 and Tamron AF18-200mm F3.5-6.3 XR Di-II LD?

I'm having Nikon D5000 with kit lens Nikor 18-55. I'm planning to buy higher lens zoom. I have short listed Tamron AF18-200mm F3.5-6.3 XR Di-II LD. My question is whether it will fit on NikonD5000 body? Wheather it will produce good images with D5000 body. Please advice.

First time working with a model: Tell me what you think about my photos?

I'm an amateur. I'm 16 and i don't have any professional equipment apart from my Nikon D90.
I got my friend to model for me, this is the first time I'm working with a model.

Please give me some constructive criticism and how I can improve.

Which 50 mm f/1.4 lens?

Http://www.amazon.com/Nikon-50mm-Nikkor-Digital-Cameras/dp/B00005LENO/
or

http://www.amazon.com/...001GCVA0U/

i have a nikon d5000 and i know it doesn't have a built in motor and i would have to manualy focus, which wouldnt be a problem. Are there any differences at all? Is one better than another?

How to shoot HDR with Nikon D90?

I just bought my Nikon D90 and want to do HDR, can someone teach me how?

Is the Nikon D5000 really THAT much better than D3000?

The Nikon is about $200 more than the D3000. As my first dsl and looking for something that'll last me and is pretty versatile, is the D5000 really worth the extra money?

Lens 18-105 VR or the pair 18-55VR + 55-200VR?

Then I'll buy the Nikon D3000 but I can't decide which kit: one goal or two… It is obvious that with the pair covered a longer focal length but the 18-105 and keep it fixed nn exchange for continuous two goals (not very comfortable and you are likely to get us into the dust) do you recommend?

Nikon D3000/D3100/D5000 which one for beginners?

Nikon D3000/D3100/D5000 which one for beginners?

Which camera has better quality? - 1

Http://www.bestbuy.com/site/Nikon±+10.2-Megapixel+D3000+Digital+SLR+Camera±+Black/9456803.p?skuId=9456803&ci_src=14110944&ci_sku=9456803&ref=06&loc=01&id=1218107268800

http://www.bestbuy.com/...&cp=1&lp=1

Nikon D5000 fog/mist settings?

I'm an amateur photographer and I can't figure out the proper settings for a show at Seaworld. I've never worked with fog and this type of lighting at the same time before, and I couldn't figure it out. Does anyone know some settings that might work? Here is a link to some of the pictures so you can see what I'm talking about: