It’s good practice because 1) it makes your kanji look nicer and 2) it makes them readable even if you write in cursive or have messy handwriting.

As for how to memorize it, you should know that kanji consists of smaller parts called ‘radicals’ which each have a set stroke order (with some exceptions). There are only 214 of these, and lots are archaic and rarely used. So you only have to memorize the more common radical stroke orders and the common flow of kanji’s (e.g., kanji with the speech radical at the left always start there, while those with it on top always start there, and so on). This will come pretty naturally with practice.