Here is a quick breakdown of hook sizes to use with particular baits. This is for general information and just a rough guide as different manufactories have there own idea of what a certain size should be. This list though will be a good starting point.
Hook size 12
Breadflake, paste, meat, sweetcorn, cocktails, chum mixer (floater fishing),
meat, mini boilie, peanut, tigernut.
Hook size 10
Paste, meat, bread crust, chum mixer, double sweetcorn, meat, maize, chum mixer, 10mm boilies, tiger nut
Hook size 8
Lobworm, paste, bread crust,
21mm pellet, meat, triple sweetcorn, 11mm boilies, 14mm boilies, 2 x chum mixer, maize, tiger nut, 14mm pellet
Hook size 6
Whole lobworm, paste, bread crust, meat, 16mm boilies - 19mm boilies, 21mm pellet.
Hook size 4
Whole lobworm, paste, bread crust,
Meat, 20mm+ pellets, 20mm+ boilies.
In more recent times we have been spoilt by the likes of ESP who have released excellent hooks.
They where also the 1st to release hooks in non traditional sizes. These being odd sizes such as 5 and 7's.
Many carp anglers do not like using hooks above size 4, fearing that larger sizes can damage a carp's mouth and there may be some truth in this. For most general bottom bait fishing situations a size 5 ESP Raptor may be all you will ever need. A wider gape pattern would be a better option for pop-up fishing. It is important to take a realistic look at your presentation and try to imagine it on the lake bed or even better still just drop your rig in a clear margin to see if the presentation is subtle.
Carp are not stupid and presenting them with a rig that looks un-balanced will effect your chances of a pick up. An example of an unbalanced rig could be for instance, using a size 4 hook with a grain of sweetcorn.
I know this is a unrealistic example but I have used this analogy to emphasize the point. One last point, never try to save hooks and re-use them time after time.
Of course re-using them is fine if they are in good condition and most importantly that the point is sharp.
Today's chemically sharpened hooks will always be at their best straight out of the packet. You will never be able to sharpen the hook back to its mint condition. Always check the hook point after each and every cast.