All the suggestion will be considered friendly as long as they are coming from bottom of your heart and for their good....

你可以说：天天锻炼有益你的健康；吃含蛋白质的食物对你的身体有好处。

I think you can just give your pieces of advice to someone directly.There is not a fixed form for offering suggestions.If you want to show your sincerity,maybe you can also provide some reasons for giving that kinds of advice.if you don't want such a direct suggestion,you can say as follows: 你是不是应该每天锻炼一下，会对身体很好。 你应该多吃点蛋白质吧，它能帮你。。。。 我觉得你最好每天锻炼，那样就会。。。。 你觉得多吃点蛋白质会不会对你更有益处？

运动有益身体健康，蛋白促进骨骼生长

生命在于运动，每天锻炼有益您的身体健康。 不妨多摄入些蛋白质，对您的身体有好处。