This one is very important. It truly does make a huge difference when wearing a suit, and can distinguish you from others in the pack who don't get it. Suit jackets look best when properly tailored, and sleeve length is usually the first place to start. Sleeves that end halfway down your palm or at your upper forearm look sloppy. Instead, make sure you wear a properly fitted dress shirt when fitting your suit jacket, and leave some room for that shirt cuff to show.
Okay, here's the first rule that I flat out disagree with. Nothing wrong with it, and I see why they see it this way, but I just have a differing opinion. I personally think your first suit should be charcoal in color. It's the most versatile, and can be worn in almost all situations where you wear a suit. The second suit should be navy, like mentioned above, as it's equally versatile and classic as the charcoal, and is a wardrobe essential. Both the charcoal and navy suits should be solid in color, with no plaid or stripe designs.
Now once you've gotten the two main basics, then you can start to branch out. Going seasonal (like tan for the summer), patterned (like pinstripes), or black (like... black) are all fair game in my opinion. I personally would still stay on the path of remaining classic, and get myself a mid-grey suit. It's still just as versatile as the others, and looks great in almost all situations. Again, I personally would avoid any patterns on this suit as well.
So there you have it, my recommendation is: First suit - Solid Charcoal. Second suit - Classic Navy. Third suit - Mid-Grey.
To be honest, I don't know that many people who wear suspenders, but either way, this is a good rule to know and lock in your head in case you do start wearing them. Wear a belt or suspenders, but not both. Quite simple as that.
Alright, well there you have it. Three more rules for all of us to keep in mind when dressing ourselves in the morning.
One thing I will mention is that the important part of all of this, is that you know the rules of style, not necessarily that you follow them. Those who have the best minds and eyes in fashion generally have the rules down pat, it's just they know how to break the rules just as comfortably. Something to think about.