and then the mix goes to shit... well ok, not necessarily, but I would definitely not start by pumping the lows. With compression, it might help to put two different compressors on the kick. The first one can just take the peaks off of it, the second can fatten the whole thing up.
On the first one try something like a 3:1 ratio, then start with the threshold all the way up and bring it down (while your song is playing) until you notice about 2-3 db reduction at the loudest part of the song. Use a very quick attack for this compressor like 5 or 10 ms with a fairly short release maybe 30-40 ms
for the second compressor use a lower ratio of around 1.5:1 or 2:1. set the threshold so that there is around 3-5db reduction max. for the attack and release on this one, you'll have to experiment a bit on your own, but I would try a much longer release to avoid that "pumping" sound... maybe 300-700ms.
For a thick kick sound as far as eq is concerned, here's a few things that work for me... first off, drastically cut all frequencies below about 30 hz. slightly bump up (maybe a few db) the low frequencies around 70-100hz (in the analog days, many producers had shown that recording to tape caused a "head bump" around these frequencies which produced a fatter sound). Now you'll likely need to remove some muddy frequencies between 200-500 hz with a pretty wide Q... don't take a bunch away as it will sound too thin, but a db or two across that wide of a range will take out the mud without thinning the sound too much. Lastly, a high frequency raise could give a little bit more air to the kick sound and in turn make it seem thicker. maybe somewhere between 3-6k. Don't get too narrow with the Q on this one as it could cause that weird "notch filter" effect, and a slightly clicky sound. Hope this helps.
BIGGEST ADVICE: just use your ears above all else. maybe these things won't work in your mix with your song. This is just what works for me time and time again with the kind of projects I work on. Let us know if that worked at all.
