750 is not really old in terms of power. I just sold mine a month ago for my sandybridge (haven't updated sig yet). Don't know which motherboard you have so I can't give you specifics.
Here's a guide that is posted in the stickies
http://www.overclockers.com/3-step-guide-overclock-core-i3-i5-i7/
I'll give you a quick idea, but its not the "proper" way of doing it. Since the "proper" way can take up a lot of time. Assuming that you have a good air cooler:
go into bios
manually set your ram to it's ratings (voltage and timings)
turn off eist, c1e, and any other power saving features (c-states)
bclk (or fsb) to 190 or 180 if your bios allows x21 cpu multiplier
cpu multiplier x20 or x21 if motherboard allows it
qpi to the lower multiplier
ram multiplier to make ram 1333 or under (for now or if you don't care about overclocking ram)
cpu voltage to 1.35
QPI/VTT voltage to 1.3
This should give you 3800mhz. If it doesn't work, try more cpu voltage up to 1.4v. If that doesn't work, try 1.33v or 1.35v on QPI/VTT then start back at 1.3v for CPU voltage and work your way up. Haven't seen a 750 that couldn't hit 3.8, except for those still running stock or subpar cooling.
You'll have to run stress testing programs once it works to test stability. I suggest running intel burn test for a quick check. Then when it passes you can run other programs to check. Keep temps under 80C during intel burn test or stress testing. Your temps should never hit that mark during regular use.
If it does work, you can then start lowering your cpu voltage then stress testing again to check stability at lower voltage. If your temps are too high, then back off on voltage and bclk (or fsb). CPU speed = bclk x multiplier.
