How to talk to friends??
This mostly should depend on the specific dynamics of your relationship with them. However - since you're asking us - my guess is that the best answer is lightly and/or indirectly. Talk about what you're doing (don't preach) - how you're investing, how that helps with your long term plans, etc.
Ultimately - it's not your responsibility to get them to make what you think are good decisions. It's their life, let them live it. Just like you would probably see less of any friend that badgered you to spend money, they probably would want to see less of you if you badgered them about their spending.