Beauty is in the eye of the beholder. Walk into an art museum - some things will catch your eye, others won't (but will catch other people's eye). My wife and I gravitate towards different sections.
I never assume I have the same definition of beauty as someone else. My daughter and I will take decidedly different photos of the same subject - mine are more technical, hers more artistic. I am an engineer, she is an artist. If she asks my advice I have to focus on what she is trying to achieve, not how I would do it for my style.
When I act as a consultant in business I find it often works to understand things from their perspective first. When asked such an open question my standard response is usually "It depends." In a situation like this I would ask a few questions before offering advice. What they were trying to achieve? What do they like and dislike about their photos? What do they wish they could change. That gives me a better basis for answering their question in their terms and help them improve what they are already doing. Sometimes I find it better to provide the advice as questions to soften the tone. Have you considered using depth of field to better isolate your subject from the background?
The other big issue, particularly with beginners, is TMI. As an engineer I can easily jump into the details. This works fine with a peer, but not so well with a person at a different skill level. It's usually best for me to offer one or two things to try out first to help them progress from where they are. More than that and they are often overwhelmed. If they like my first comments, they will come back for more advice later.
Responding in a forum is a whole other matter since there are many different definitions of beauty, photography styles, and skill levels. Some may be fine with the advice and find it helpful. Others not so much. It really comes down to knowing the audience really well and addressing everyone, not just the OP. This is something we all struggle with, even in this forum.