A lot of skill gems are much better once they have +20% quality, and there are a few ways to get your skill gems to 20 % quality. You can firstly be extremely lucky and find a 20% quality version of the gem you are using, but most people need to use one of the following methods:
1) Use Gemcutter's Prism to level it up. Each Gemcutter's Prism increases the quality by 1%, so you will need a total of 20 of these for each gem. This currency is very expensive, so getting 20 % quality gems by this means is pretty expensive.
2) A cheaper alternative is to use the vendor recipe that gives you a 20 % quality gem. For this you need a level 20 gem, so you need to level it all the way up to 20 to get this recipe. Sell this gem to a vendor along with 1 Gemcutter's Prism, and you get a level 1 version of the gem that is +20% quality. This is much cheaper, but the downside is that you need to relevel the gem to 20 again to get a full effect from it.