Now, posting this on TFL might be a bit like teaching your Nanna to suck eggs. or blow eggs. or whatever the phrase is, I forget.
But too bad, I'm posting it anyway :p
A few points first. Get a good knife, and know your loaf. I have two knives I use for my sandwich loaves - one is quite harsh on the bread and is no use in a soft bread, as it rips it apart. The other is great on the soft loaves, but just doesn't work well in the firmer styles. Practice makes perfect - you come to know what your knife will cut, and what thickness you can slice with it.
It's interesting though - I find if I stand straight in front of the loaf, square, I can never slice even slices, I always stand a little side on to the bench, and it works. It's probably different for you though!
grab that loaf, and put it on your favourite cutting board. Don't tell me you don't have a favourite... I guess that's just me then.
When making the first slice, you have to remember that most loaf tins aren't square at the end, but slope out a fraction. So your first slice will be thick at the top, and thin at the bottom. Use your finger to mark where you're going to slice...
then slice! once the knife has just bitten through the crust, slide your fingers over to hold the slice steady whilst you cut the whole way down. If you choose not to do this, it's a lot more likely to get slices that are thick at one end and then at the other.
Keep an eye on the knife the whole way down, it takes concentration to cut it straight. I prefer not to correct if it's going astray, but that's just me.
When you reach the end of the loaf, it gets a little trickier. Here's how I do it:
however you could also lie it down on the board and cut horizontally (very carefully!)
and you're done. sit back and admire your hand carved, beautifully even loaf.