What can I expect to see?
The most important moment is when Venus touches the inner edges of the sun. Look for the “black drop” effect, when Venus sometimes appears to elongate near internal contact. It is a phenomena that has frustrated astronomers and explorers since 1761. Because the edge of Venus sometimes smears against the edge of the sun at this moment, observers have had a tough time estimating the exact second when contact is actually made.
When looking through solar filters, also look for sunspots scattered along the mid-section of the sun. Notice how these solar blemishes often have a dark central portion (umbra) within a less intense sunspot outline (penumbra).
When the sun is at the horizon, you may also see phenomena of colors, as noted by Steven van Roode at http://transitofvenus.nl/wp/2011/12/20/reversed-colours-of-venus/.