My experience is, 'helping' in this way is very rarely successful. Usually the person KNOWS perfectly well what they could/should be doing. Usually, lack of action is a personality trait, or a habit, and changing the pattern depends on what motivates each person. That is really hard to affect from the outside.
Successful external pressure, I think, is rare. First, you have to understand the barrier to the person acting, which could be physical (pain, injuries, unsafe or unpleasant outdoor environment for walking, etc.) but is most often psychological (procrastination, passivity, poor social modeling from peer group, lack of mindfulness, poor habits).
Many people have trouble figuring these two elements out for THEMSELVES, let alone for others. And even if they do, they then have to figure out concrete steps to address the barriers.
I think the strongest external motivator for most people is a serious health scare, or consistent sustained support/pressure from their immediate social group (e.g., everyone at work committing to only healthy snacks in the breakroom; everyone in the social group wanting do active physical things like hiking during social gatherings, increasing the pressure to be fit enough to do so, etc.).
When I've tried to motivate passive people who say they want to act but never do anything but talk, the single thing that I've had any success with is to do the thing WITH them. I mean, actually physically showing up and doing the thing in their presence. Make a date, show up, and do the exercise WITH the person. This tends to work with diet only if you live with the person. Either way, it essentially means that you must take on the same project yourself, and commit to it the same way you hope the person you are motivating will. The downside is that as soon as YOU stop doing it, the person you are trying to motivate will likely slack off as well.
Verbal advice/pressure, is in my opinion, of very little help, unless someone is already actively eating better, working out, and wants new ideas or tweaks for their program.
If motivation were as easy as long distance encouragement, we'd all be healthy and fit.
