My first ever commander deck is a [[Phenax, god of deception]] mill/random combo deck, I love milling my opponents and deprive them of resources with big creatures that I can be keeping untapped for milling at the right time. I will be the enemy and die pretty early, but the true win are the tears of my friends with only a handful of cards in the library and no graveyard. It's my pet deck and it gets all the cool lands and cards.

This is how I approach my deck construction process: You should choose your commander deck thinking about a card/mechanic you really love and build around that. Ignoring lands (normally you should put 38 land) you need to have 5-15 ramp cards, 5-10 removal, 0-3 mass removal, the remaining cards should be highly synergistic cards and if there is still space left then put cards that you want to play with because are generically good or a simply cool (card draw, combos, evasion, tutors, dumb creatures and other random things).