> Chopping an onion takes what feels like an eternity.
It's definitely partly practice, but make sure you have a decently sharp knife (you don't need to get anything ridiculously expensive but you should be paying ~£20 for one knife). The cheap "sharp knives" you get for £20-30 for a whole set tend to not actually be that sharp and make it really difficult to cut through things like onions because they slip all over the place.
I got my high quality but very old knives professionally sharpened a few months ago. It made a world of difference and cost something like £25 for 5 chef's knives, scissors and a serrated bread knife.
The guys I went to (in south London [1]) do most of their business renting knife sets to restaurants: each chef has two sets of knives; every few weeks they come by to drop of the newly sharpened set and take the other set away to sharpen back at their workshop.
Their tip is rather than paying full retail price for quality knives, buy knives through them. They'll recommend what's best for your needs and budget. You can save even more by buying from their restaurant rental stock, freshly resharpened, for something like 1/8th of what you'd pay new in a store.
[1] http://www.collini.co.uk/ in Balham (55 Fontenoy Road, SW12 9LX). If you take your knives to them for sharpening, you can watch them do it, on large, 1950s era motorised grindstones. Absolutely fascinating.
It's definitely partly practice, but make sure you have a decently sharp knife (you don't need to get anything ridiculously expensive but you should be paying ~£20 for one knife). The cheap "sharp knives" you get for £20-30 for a whole set tend to not actually be that sharp and make it really difficult to cut through things like onions because they slip all over the place.