I have a friend of mine, just before a big challenge. I would like to pray for her somehow. How to do that and what exact tehilims should i say?
I have been told by my rabbeim in Atlanta and Passaic to either
- read the entire Sefer Tehillim cover to cover, yourself or dividing it among a group; or
- pick a set of psalms with resonating themes (ones usually used are 121 and 130, sometimes 20, 23, and many others);
and say them yourself repeatedly, thinking over them carefully as you say them, and have your person in mind among other ill people of Israel. If you say in a minyan responsively, it is common to also add a mishebeirach, a special prayer for the welfare after saying them, either in their merit or in the merit of you giving tzedaka for the speedy recovery.
Let it be His will to bless your friend with a speedy recovery soon.
You can always say the "Tikun Ha'klaly" - a collective of 10 tehilim chapters Rabbi Nachman recommended saying as a 'tikun'.
The chapters are: 16, 32, 41, 42, 59, 77, 90, 105, 137, 150.