Hmmm..The sound you are probably getting is from the amp is buzzes, squeaks, or rattles right? If this is the bad sound. It's the amp and the only remedy for this is to try a different speaker, or a different cab altogether.

Another reason for bad sound could be because of the room ambience. Plus, with using a condenser mic that picks up alot of room ambience. First, you shouldn't use a condenser mic as the close one to the speaker. It just picks up too much, use it as your distant mic and the sm57 or any other unidirectional mic for close miking like trendkilla said. Back to a remedy, try moving the guitar amp into another room, good rooms include the following.

1 ambient guitar- tiled bathrooms, hallways, or large kitchens with tiled floor.
2 semi-ambient guitar- living room, bedroom.
3 non ambient guitar- closet.

Since using most of these rooms is probably a mess in itself, try throwing a blanket over the mic and amp. This will control the ambience, which if needed you can later add with reverb or echo.

Another thing is take off all the effects on your amp, reverb, echo, whatever. Except compression if you have it, but don't use to much. Just enough to balanced the sound, you don't want a crushed guitar sound. Mess with the EQ on the amp, to get a good sound from the amp first, then mic it. Try different distances until you find you that has a nice complete bold guitar sound. The distant mic should be 4-5 feet away and about a foot above the speaker.If you use a distant mic, lay a blank on the floor between the amp and the mic. Now ajust the volume level of the amp to comfortable level for the (close)mic, too loud and the mic distorts, too soft and mic won't pick anything up.Then use the trim to boost volume of the mic. Use the noise gate on the mixer, set it to where if you set your hands on the string you can't hear it, but as soon as you start playing even lightly it is picked up. Then try it.

Hopefully you have a mixer, to EQ the mics. It is crucial if your going have a half way decent recording. Here are some guildlines to start with.

Close-Mike
add clarity boost 10k
more strings boost between 5-8k, careful
more edge to sound is around 2-3k, boost very carefully cause too much will cause a lisp
the body is at 500 hz
the grunt is at 100hz

if you use the distant mike boost it at 10-15k and cut at 200hz.

When mixing down the EQ range to best concentrate on are 100hz, 500hz, and 3k.

Another good way to record, is directly into the mixer instead of miking the amp. You will get rid of all the bad sound from the amp and room. The only bad thing is it will sound very thin, so it's best if possible to record both miked and direct.

Also, your probably not gonna get the exact sound you want. Just worry about getting a nice, clear sound when recording the guitar. You will be able to mess around with it afterwards to get the sound you want, when you add reverb, EQ, whatever you wanna do.

Hint. DO NOT APPLY ANY EFFECTS WHILE RECORDING, SAVE IT FOR WHEN YOU MIXDOWN.

I hope this helps.