dog-walking tips for the dim-witted

I have signed on to walk a friend's dog while she is training for a new job. She is 1-2 years old spayed lab cross and has never had any formal training. My friend has taught her a few basic commands (sit, stay, etc.) which she obeys, but only with a great deal of prompting.
I have been out with them a couple of times just to watch her in action, and frankly the dog is a bit of a nightmare on the leash, constantly pulling in all directions. She gets lots of 'playtime' but never really long walks, since my friend has a bad back and can't go long distances.
Unfortunately, any broader strategies I might suggest would not be well-received, but even if we just work on a couple of things while I'm with the dog, to make our walks more pleasurable, it would be a huge help.
Although she is frequently off-leash in the park, this will obviously not be possible when I have her.

that's really nice of you to help out like that

just my own personal opinion here, but I'd probably try a Gentle Leader or a special harness ("easy walk" made by same company who makes gentle leader) to alleviate some of the pulling to start. Once you have some control, then work on the dog's leash manners each time you walk him.

I train using treat-rewards, so I frequently carry a pocketfull to reward the nice loosh-leash walking.

Tenderfoot has posted in the past some great walking advice, maybe search through and get some expert training tips to implement on your walks.

if you teach the dog good leash manners, your friend will probably have an easier time w/ the bad back.

I would suggest the Easyway headcollar if your friend would consider purchasing it. It`s been talked about in a couple of the other threads here. I think it would be a big help for your friend as well. If she has a bad back she would probably enjoy her walks more because the dog wouldn`t pull and they say walking is one of the best exercises for those with bad backs.