Newbies are a mud's lifeblood. Muds that do not provide a welcoming hand to newbies deserve whatever they get -- we all hear about these muds, but they rarely last long. There are a number of things builders can do to foster newbie friendliness:

• Don't put high level areas next to low level areas. Segue into them. Provide lots of buffer zone, and lots of warning. I quit a mud for doing precisely this. I just got sick of being blindsided.
• And while we're on that topic, don't don't don't put high level mobiles into low level areas, especially and particularly guard types. Keep the level range consistent, for both objects and mobiles. Objects should not be so cool that higher-level characters come in and plunder the area before lowbies can get in there every repop.
• Low-level objects in high-level areas is also a mistake. It will encourage high-level players to give away the objects, and worse, newbies to learn to ask for those objects; you hopefully don't want a begging economy to start!
• Have a consistent theme and areas that fit that theme. Super-dangerous-sounding fights between good and evil probably shouldn't happen at the newbie level. Newbie mobs should be less intimidating than higher-level mobs.
• Objects should reflect level. "Thor's Hammer" probably shouldn't be level 5. "A pointy stick" probably won't be level 99. High level players like having cool-sounding gear, and who can blame them?
• When it comes to armor, be consistent. There's no WAY a linen robe could give better protection than a coat of mail. Newbies don't have much money, so they judge effectiveness by intuition. Let your newbie gear, at least, be logically consistent. When players hit the high levels, then let the magic armor rule, where "tightly-fitting purple tights" are much better to have than "ice-steel leggings".
• Color is evil if it is inconsistent. Go for consistency. Eschew the "kewl". Color can either be an aid to gameplay, when it's consistent, or a distraction, which all too often it is if inconsistent. It can be a visual nightmare when every noun in a room desc is pure white or neon green, or if your players look like strings of Christmas lights. I seriously would advise builders not to sprinkle color around unless they're absolutely sure it won't detract from readability and consistency.
• Don't put cutesy death traps in newbie areas or in newbie towns. They're not half as funny as people think they are, and many admins and mud philosophers now feel that they discourage exploration.
• An area full of gear is a good idea at the low levels, even at the newbie levels. Newbies don't like running around in only a leather vest/leggings and sandals. They like having lots of wearlocs covered. Also, if a character finds himself naked, through death, PK, or whatever, he has a fast way of getting a few things to re-equip.
• Behave in a professional manner on communication channels and in email. Say "thank you" to your builders every so often. Behave professionally toward area proposals and potential recruits. Give credit where it is due.
• Reconsider your decision to use the venerable Newbie School. The first muds I ever played didn't have it, and we got along just fine. Newbie School is a cute area, but it's old, we've seen it, and it doesn't add to YOUR mud's theme. If you must have one, and insist on not customizing it to your mud, please don't force newbies to go through it. A newbie school is, at best, something that can be accomplished more elegantly by an original area, and, at worst, patronizing and belittling to experienced newbies. Is either something you want?
• Make your start town logical to travel. Amorphous areas that feel like they were written on an online editor on the fly do not appeal in the slightest. Consider making it fairly small. Clearly mark dangerous and shady areas. Keep aggressive things out of the town.