This question has been asked many times on this forum and is a practice ive been interested in perfecting, so ill try 2 compress past posts ive read into this one. Whot a bloody nice bloke i am.
First off, the type of sample your using has a huge role in providing phattness and making the kick really KICK. The 909 drum machine by roland has legendary kick synthesis and has been used for many years by top hip hop,DnB and house producers. You dont have to have one of these machines however, cause it has been sampled so many times and the internet is crawling with 909 samples. Also most software drum synths have 909 emulators. Personally i have Waldorf Attack which produces some good 909 kick waveforms which can be tweaked to perfection.
If the 909 sample sounds too round and bland for your tastes, a live kick sample can be pasted over the top of your sample with its bottom end rounded off to give the kick more expression.
But theres no beating the 909 for bottom end boom.
EQ can play a important part, (as it can with any sound). If the sample lacks bottom end a boost of around 6db at 80-100Hz will sort it out.
To get that thwack, boost (sparingly) at 300Hz, or you could use extreme compression with a slow attack.
Another trick is to mix the kick with a very short delay of around 3 milliseconds to produce a sort of comb filter effect, this can work well, again if used in moderation.
I try not to use too much compression on my single samples, but try to get them as close to the desired sound by using the correct samples EQ and FX. If my kick is close to perfect i use compression with an attack of 20 ms, to let the initial transient through before the compressor kicks in, i use a ratio of 5:1 and only 10db of gain reduction. This setting reduces the dynamics just enough to tighten everytin up.
A good tube distortion effect can also add life to all frequencys of your sample, as it boosts the harmonics of every fundamental frequency. Again use very sparingly.
Last word of advice. Many people (myself included) spend so much time trying to get their kick to really pound that they neglect the top end of the freq spectrum. Monitoring your mixes at a low level can ensure the kick cuts through, if it dont boost at 2-8kHz.
Good luck with your quest to find the perfect kick, im off to soak my blistered fingers in hot water.!
PEACE