How can I make proper sandwich slices of home-made bread?

You can buy a home bread slicer - and you can also make one.

"My little invention works on the same principle as a carpenter's miter box (as a matter of fact, I got the idea while watching a carpenter friend cut some miter joints). The only difference is that my device was made specifically for slicing homemade bread. Just slide a loaf into place, position the blade of a long, sharp knife in the slots, and you can't help but cut straight and true." - John Shell, Mother Earth News March/April 1978

I find that a rediculously sharp serrated blade is the key -- I have a Wüstof bread knife with what they call a 'wavy edge' -- it looks more like a scalloped edge. I find it goes through bread much cleaner than a standard serrated knife. (if it has a soft crumb, it don't end up with the surface of the cut looking chewed up).

You also want a knife that's fairly long -- you want to take nice, long strokes with very little downward pressure; if you can, just blade slowly fall through the bread as you push it back and forth. Short strokes will end up with more of the 'chewed up' look.

I also find that the type of bread, and how you store it can be significant -- if the crust is too hard (eg, non-enriched breads), I find it more difficult to make a sandwich from it. I keep loaves that I know I'm going to be slicing thinly in a plastic bag, so the crust doesn't overly dry out (eg home-baked or those from the farmer's market they sell in paper bags or perforated plastic bags, I throw 'em in a plastic grocery bag when I get home, so it doesn't dry out in 24-48 hrs). If you have a bread box, that would work, too.

... and if none of those tips help, there are knives with 'slicing guides' available in a range of prices that have a parallel bar to help give you a reference so you'll slice more uniformly. To use them, you need a slightly different technique; as the guide protrudes past the blade, you need to make the last pass with only the tip of the blade.

You may find that an electric knife (not a full electric slicer) makes it much easier to slice bread thinly, as the back and forth action saws through cleanly and you don't have the tearing or pulling that may happen with a regular knife if it is not perfectly sharp or used with perfect technique.

If find that using mine makes it easy to make small croutons every year for thanksgiving stuffing.

Something like this:

This works well for me: http://www.amazon.com/EdgeCraft-610-Choice-Premium-Electric/dp/B0002AKCOC and I can slice meat and cheese too!

My wife suggested using our electric meat slicer. I did and it worked great.