Stay away from pre-amps except as a last resort.  The little Winegard HD-1080 8 element antenna will probably serve you well and it's short enough to be mounted in an attic.

If you already have an attic antenna, most likely it has UHF elements and you don't need to do anything if it's close to the reciever.  Move it closer if possible.

I'm running a loop hanging from a hickory ram rod on a stand so it can be turned easily.  My kid thinks it's ghetto.  I think it's engineering elegance.  In any case, the point is to try simple and low cost first.  Keep the indoor antenna as high as possible and away from aluminum window blinds.  An outdoorr antenna at the same height just outside the wall where the reciever is located will have a bazillion times more gain than one just inside the wall, and can be mounted on a short and low cost mast for a one story house.

If you're a long way from the station, the only solution is to get a big antenna as high as possible.  UHF signals are line of sight and if you're over the horizon from the transmitter, you're out of luck.

There are plans on the net for a good 8 element home made antenna.  A simpler solution is to buy 4 bow ties from Radio shack and gang them on a nonconductive mast with 7 inches of spacing and the elements wired so the signal is in phase at the tap.  (Use the same wiring arrangement in the on line plans.)

Antennaweb.org will tell you everything you'll want to know about the location of the transmitters close to you; the distance and the azimuth from each transmitter to your address.

If you're in the middle of separated transmitters, you may need to set up more than one antenna, one centered more or less on each cluster.  The lead ins from the antenna should be different lengths if both are going to be attached to the converter at the same time, a quarter wavelength different from each other and off hand I don't have a number handy, so just make one lead 3.4th's the length of the other to start.

Trees, buildings, siding, weather, elves, and just about everything else screws with these signals.  When my loop is mounted close to the shades, it becomes too directionalized to receive more than about 2 channels reliably.  Right now it's about 30 or 36 inches directly above the set and receives everything but the PBS station which had to be located 15 degrees off the most southwest of the rest, and probably has gerbil power.

Here's the basic homebuilt antenna.  You'll find variations all over the internet.  The foil reflector is ghetto if it's hanging in the living space.  It's so cheap to try that you can't lose:
http://uhfhdtvantenna.blogspot.com/

http://www.avsforum.com/avs-vb/showthread.php?p=13920561#post13920561

The AVS forum has only about a bazillion designs and links.

Here's one that is more complicated:  http://www.qsl.net/va3rr/hdtv/HDTV.htm