What's your best diet/fitness advice?

Never stop.

#1 diet advice: don't hate yourself for having an off food day, just wake up tomorrow and start over!
#1 fitness advice: get up and get your workout in even if you can barely move... you'll feel better when it's over and it helps with the stiffness!

Take from this what you want:

I do not have before and after pictures.

But.

I've been training a young lady at the gym for the last month. I met her on MFP about three months ago, maybe a little more. She PM'd me, asking about heavy lifting and what kind of lifts she should be doing, etc. She was a member of another gym, and had her own personal trainer, but her results weren't what she wanted. She is a floor nurse, working 3x a week for 14hr shifts. She'd been exercising since the middle of March (lots of cardio, bodyweight at a park, gym 1x a week, and lots of hiking) and had lost some weight...but she said her clothes still fit her poorly, and she didn't really have a 'good' feeling about her weight loss. I told her what to tell her trainer...who basically refused. She'd tell him 'I want to lift heavy!', he'd say 'Ok...but we need to work on your form first'...then put her on machines with stupid light weight and hundreds of reps.

Machines don't teach form, first...and low weight/high reps do not make for an effective workout.

Anyhow, she messaged me back a bit later, told me what he was doing. I told her to get another trainer...she went to the management at her gym, and complained. There was a huge mess, in which the MANAGER stated to her that the freeweight area where she wanted to lift really wasn't for women, unless they wanted to bulk up (understand, this is an LA Fitness in Phoenix spouting this crap). After enough fight though, they gave her another trainer. He was no better. She was lifting with him one day a week. He would have her do cardio for an hour, then ask her what she did for exercise during the week...at which point he would throw random exercises at one body part or another. One week it might be legs, the next chest...etc. He would KILL whatever body part he was working...flooding her with reps on ten different machines for her hour of training.

She messaged me again. I told her the trainers she was working with were idiots, and she needed to be on a SOLID, FORMATTED PROGRAM, that would have her lifting heavy weights, with a progressive upload scale, and set parameters. She sarcastically (in a friendly way) asked me if I could do better. I told her to quit her trainer and come lift with me for just a couple weeks, and I would show her results.

This is the time line of her progression since she started exercising:

3/15 - 186lbs size 18+ - Started calorie counting and being active with walking outside of her work.
4/9 - 174lbs - Started hiking in addition to work and walking.
4/21 - 171lbs - Lifting 1 day a week (high reps, low weight) with a trainer, 1hr of cardio with trainer, working (floor nurse), hiking 2x a week, bodyweight 1x a week.
5/26 - 165lbs - Started intermittent fasting at my suggestion. Her trainer was VERY unhappy about it. Her food intake regulated (she was eating at a consistent deficit previously, but the amount was ALL OVER the place), and her total caloric intake increased on average.
6/1 - 161lbs - Lifting 1 day a week (high reps, low weight) with a trainer, 1hr of cardio with trainer, working (floor nurse), hiking 2x a week, bodyweight 1x a week.
6/25 - 159lbs tight size 12 - This is where we got rid of her trainer and she came to lift with me. I put her on a program based on HEAVY dumbbells/compound movements/some machines, and hitting every body part 3x a week. I cut her hiking to preferably only 1x a week, and her ONLY cardio is 10 minutes of warmup for lifting. We cut off the bodyweight as well, as I wanted her time for lifting. Overall, her activity DEACREASED.

7/27 - 154lbs size 6, she posted this on my wall this morning:

Been a little over a month since I started lifting heavy. When I started I was in a tight (very tight) size 12. Last nite got into a pair of my old size 6 jeans. Scale has been bouncing around the same 6 lbs. Measurements havent changed much. THANK YOU. I havent worn those jeans in years. This **** works even if the scale doesnt change.

ETA - About two weeks ago, we ditched a lot of the dumbbell work. Lori's balance with dumbbells was poor at best, and her form was impacted badly. We integrated barbell squats and deadlifting (I know, you would think this would make balance worse...so not the case with her)...and her gains have literally skyrocketed since.