If you have already heard of תדיר ושאינו תדיר תדיר קודם -- frequent and not frequent, frequent first -- and are surprised by the title, you are welcome to skip to the end, but please hear me out. If you are not so familiar with the topic, let's start with a short introduction. In those cases where two obligations come up for a single event, this rule determines which comes first. For example, in bentching there are additions for both Shabbos and Rosh Chodesh. On Shabbos Rosh Chodesh, you will perforce say one before the other; halacha neither requires nor even condones speaking different things out of both sides of your mouth. The rule of תדיר ושאינו תדיר תדיר קודם tells you to say the addition for Shabbos first, and then the addition for Rosh Chodesh. This also comes up in the chapter of psalms we say after morning prayers. The extra psalm for Rosh Chodesh -- which is said 18-ish times a year -- comes after the daily psalm -- which is said 52-ish times a year. What about לדוד/Psal...
This is a paraphrase of the pasuk in t'hillim 84:7 -- "mei'chayil el chayil" -- which means "from strength to strength". In this case, it is my thoughts and ideas to those who are strong enough to be interested :)