You might review my PHD guiding struggles here....
http://www.iceinspace.com.au/forum/s...ad.php?t=18092
Som of the tips that worked for me, sort your mechnical and aligment issues out first then in no particular order...keep you correction speeds below siderial, turn backlash compensation off in the controller and software, calibrate in the region of sky you are going to guide in, do not saturate your guidestar image (can cause centroiding issues), consider slight defocus of guidestar, guide in one direction only for DEC (opposite the residual drift), unbalance your mount a bit to the E and rebalance after meridian flip...keep your guidelogs and review after each session.