I had problem with ableton at first too. And Im still missin one simple button like - beatmatching
that's why beatmatching is still and will always be manual work, in my book at least
anyway, i'm doing it like this:
1) drag the mp3 file into the audio track.
2) double click it to open the sample/waveform view in the bottom pane.
3) there should be no warp markers (the yellow markers) now, only one on "1". if there are any, right click the "1" and select "warp from here straight", that should clear all others.
4) move the "1" marker to the first beat, or whereever you want to warp from. zoom in to make sure it is set exactly
on the beat.
5) on the left side (the "sample" tab), where you can enable/disable "warp", it should show the detected bpm. in the best case, this should be a straight number like 135.0. if it isn't, the track might be a vinyl rip or something. if this number is off badly (misdetected, like 180 or some odd number like that) and you know what the actual real bpm is, you can adjust it. nifty tool: DJ BPM Counter
6) right click the "1" marker and select "warp from here". this will use the bpm from the left tab for warping. alternatively, you can try the "warp straight" thing. another thing you can try is set ableton to the bpm of the track (top left part of the screen, global bpm setting), and then use "warp from here starting at xxx bpm". play around a bit until you get a close match to the actual warping you wanna do. make sure it doesn't add a whole lot of the yellow markers into the track, there's a good chance they're not put correctly. it's better not to have any yellow markers added automatically at all and instead put them in yourself manually.
7) now comes the manual work: zoom in to a place further into the track (like 8 or 16 beats, i.e. the "9" or "17" marker or any other good place). unless the bpm and the automatic warping are perfect, you'll see the marker to be off beat by a bit. now double click
the marker to make it turn into a yellow warp marker. now you can move it and set it exactly on the beat, like you did with the "1" marker. only the yellow markers
will stay fixed at their place, the other ones will be moved flexibly and automatically between the yellow markers.
8) continue this with other places (marker 33, 49, 65 etc) until you're finished to the end of the track. you don't have to do this for all the beats, it might be enough just to do it for the "1" and then somewhere in the middle of the track (like on the 129) and then again somewhere near the end of the track (e.g. 257). it depends on the quality of the track. for making mashups with analog sources (like the sample from samim - heater), it may be necessary to set a manual marker on every single beat there is.
9) practice and enjoy
let me know if something isn't clear, i can post screenshots then.