Extending China Visa, clarification please!!

It's usually easier to do in a mid-sized city. Neither major cities like Beijing nor thumbnail-sized towns.
Yes, you'll need to do it when your visa is almost due to expire. If you do it early, you'll just lose the number of days you had left originally. Ie if you get it done on the 5th day of a 30-day visa, you'll lose the remaining 25 days.
Cheers!

dont extend in beijing or any really big coastal city. provincial capitals are usually good (except lhasa), but regional centres seem the best, the more obscure the better ive found as they are so bewildered by a foreigner they tend to dish out the hospitality and give long extensions.
with enough of a reason you can ask for up to 90 days.
some places go thru a big thing with photos and interviews and it can take a few days, whilst others just bang it out on the spot. prices depend on nationality and the process involved. take some photos just in case.
dont expect much english, but so long as you are on the good side of the PSB they are usually quite friendly. things like foreign cigarettes can help.

Thanks so much for responding so quickly! And thanks for the tips, stoognik...I'll pack plenty of smokes to share!

ellyse, I always enjoy reading your helpful responses. You are gem here on this forum!

Also agree with the provincial capitals. The PSB in these provincial capitals will generally be friendlier and more helpful (don't believe I just wrote that about the PSB).

I second the more obscure the better comment in #2. I've gotten extensions in Jyekundo, Qinghai and Hailar, Inner Mongolia, both issued on the spot.

Thanks for the compliments #3, I try my best. :)
Cheers!

Be aware though, you have to give up your passport and they give you a paper receipt which is not good for anything official, checking into a hotel, getting money, etc. They could have it two days to who knows?