Meta keywords aren't used in any search engine any more as too many marketers decided to keyword stuff to gain the upper hand in terms of their SEO. To be honest I'm not even sure why the option is still there in some cases to add meta keywords anymore as they are redundant.
The meta description is only important to affect your click through rate (CTR) when your pages rank. This gives the potential visitor a reason to click on your link from the Search Engine Results Page. It should be appealing and give the visitor a reason to click on the link. A good rule of thumb and something that I've found particularly good for CTR is to write a short passage and then leave a few words out as a sort of cliffhanger. For instance if I had a page ranking for a new computer game term then I would put the meta description as something like..."The all new Mega Man 15 now comes complete with the very best...".
It's a terrible example but you get the general jist.
Now that you've read this the reply, the question you should really be asking yourself is 'Does your CTR affect the ranking when in the top 10 of SERPs?'