From what I recall of my old C2Duo, the base clock will stay the same and the multiplier changes. This holds true for my Intel Ivy Bridge processor as well. However, the way Intel Sandy Bridge / Ivy Bridge overclocks and the way "older" Intel and AMD processors overclock are different.
Depending on what processor you're using, you might want to check out these overclocking articles:TR's guide to overclocking.Overclocking the Core2 and Athlon type processors.
If you own an Intel Sandy Bridge or Ivy Bridge processor (only the K-Series processors are overclockable), you'll just be changing the Maximum CPU Multiplier, but the rest of the process of checking stability stays the same.
If you're new to overclocking, I would NOT recommend increasing any voltages to regain stability. This has detrimental effects on the life expectancy of processors. It's fairly easy to google an overclock for your specific processor, just make sure you're paying attention to temperatures with something like HW-Monitor
For an "everyday overclock", I would back off once you get up around 65-70C while running Prime95
even if you're still stable. Feel free to ask for help here at TR. If so, make sure you provide as much info about your system as possible: motherboard, CPU, RAM, etc.
Main: i5-3570K, ASRock Z77 Pro4-M, Asus GTX660 TOP, 500GB Crucial BX100, 2 TB Samsung EcoGreen F4, 16GB 1600MHz G.Skill @1.25V, EVGA 550-G2, Silverstone PS07B
HTPC: A8-5600K, MSI FM2-A75IA-E53, 4TB Seagate SSHD, 8GB 1866MHz G.Skill, Crosley D-25 Case Mod