Certain questions keep coming up within the MNM group.  I’ll post helpful links and answers/humble opinions on this page.

How do I know when to mulligan?

These articles put it nicely :
Magic the Classrom : Mull it Over
The Art of the Mulligan

Where do I start when constructing a new deck?

First thing is to have an idea or theme for your deck. Control my Opponent’s plays, Aggressively Attack with as many creatures as possible, or Use Elves are all good examples. Then, I start with the Rule of Nine to pick the key spell slots. Beyond that… test tweak test and repeat. I’ll write up a post on testing strategies sometime soon.

How many lands should I put in my deck?

This will depend on the number of colors, the mana curve and the number of mana producing / acceleration sources in your deck. Any deck should have enough land to ensure drops on the first three turns – meaning at least a third of your deck should be land. 23-24 is the standard starting point for 60 card decks. 17-18 for 40 card formats.

I still seem to get mana screwed every game. Any tips on how to avoid this?

First of all, spend some time practicing your opening mulligan while goldfishing. See the article above for more on Mulling properly. Also, pay close attention to your deck’s mana curve. Here’s another good article on understanding the Curve.

Goldfishing?

Testing decks against a non-opponent to see how long it takes to win. If a deck averages more than 5-6 turns, you should tune it to see what’s wrong. Here’s an article explaining this and other MTG vocabulary.

I don’t get what makes [Moxen], [Black Lotus]… etc such a great card?

Here’s an article that explains the overpowering nature of many classic cards.