What "not to worry" about

1. Grains: Grains are a reality when you hike up ISO so that you can shoot at smaller apertures and higher shutter speeds. It happens in film and it will happen in sensors but softwares today do provide lot of options to reduce grains at high ISO, but you will lose some sharpness

2. Sharpness: You should only worry about not getting camera shake and not getting focus right. If both these are absent then the sharpness is more a result of the lens you own, the aperture used and where your subject appears in the frame. For good DOF at given apertures read about "hyperfocal distance" on the net. Edges are often less sharp than the center but then if you compose by the thirds then you obviously do not have the subject in the center

3. Lens: Again as long as you are shooting to post photos on the web or printing up to A4 do not worry too much about the lens you own. Most lenses today are pretty decent. If you are going to make money by selling photos you can worry about the lenses you own

4. Color, contrast etc.: Nowadays Photoshop and the likes give you all options to enhance color, contrast, levels, shadows, highlights etc. so invest in photoshop rather than a $1000 lens or lenses

What should you worry about:

1. Composition: This is the "art". If you get a chance take a look at "Raghu Rai's" book on photos of the Taj. They are grainy, not too sharp and could be better in terms of contrast BUT the compositions are flawless. You see angles of the Taj you never imagined. Each photo is a timeless classic. It tells a story

2. Shooting the moment: In your pursuit to get the science right don't miss the right time for the shot. Lot of shots are about capturing the moment. Just shoot the moment

3. Framing: Before shooting take a split second to look through the whole frame and 99% of the time you will find you can avoid or include something and re compose. Most amateurs look only at the subject through the viewfinder and get a lot of distracting elements in the picture

4. Get the Horizon STRAIGHT: For god's sake keep your sense of geometry intact before you shoot. so many good shots look horrible because of a tilted horizon (unless it is intentional and adds value to the picture)

5. Common Sense: Think for a few minutes before you embark on a shooting session on what you will shoot 90% of the time on that day and put on that lens. Pre-set aperture/shutter speed (whichever is relevant), custom functions and ISO so that you spend less or no time in camera adjustments