1. Simplicity
Less is more. If you can say something with fewer words: do it. Rules two and three out of George Orwell's six rules for writing have to do with cutting out the crap and they are as follows:
- Never use a long word where a short one will do.
- If it is possible to cut a word out, always cut it out.
2. Get rid of "cool" in disguise
Just saying the word "cool" isn't helpful or constructive. Saying "I really liked [general part of the level], it was pretty good" is the same thing but with more words. Saying that you simply liked a general feature of the level is not as helpful as when you point to a specific and comment on it. This tip is better suited for reviews than replies, so this isn't that strict of a requirement and sometimes it can't be avoided for average levels.
3. Give Direction
If someone's level sucks, and it's among their first few levels; let them know the level sucks and then point them in the right direction. Declarative statements are pretty controversial on this forum, but it's best to let people know that their level is "terrible" not that there's "room for improvement." There's room for improvement in every level, and most of the time new people know that their level can be better but not how. Point out everything that's wrong - screenshots help - and tell them to check out "Average" and "Pretty Good" in the archives and to play more before making more. Remind them of the golden level design tip which is "If Nintendo wouldn't do it, neither should you" and set them on their way. Immersion is a much better teacher than you will ever be, so use it.
4. Stay Subjective
Opinions of anything are subjective so operate under that impression instead of trying to put on some show like what you're saying is objective. There are things that can be done objectively right or wrong, but it's not enough to describe a level's quality. Don't worry about bias because you're already ignoring levels you're biased against and playing what you like. For instance when I see some kid post a boss rush or something like that, I skip over that shit. Bias is unconscious so just operate under the assumption that the level designer thinks you're interested in a level enough to download it and respond than trying to water down what you have to say.
5. Ignore bad responses
Don't ignore negative reviews, they're there to help you improve. Instead avoid responses that don't match up with these little lessons, and especially so if they have a paragraph or more about graphics you use. This is how we get to people thinking you need custom graphics to make a good level, or cutoff/clash is objectively bad, and brings everyone to make the same type of level where the only changes between them are the graphics. Some of the higher ranking Community Contest winners have put shit into their levels that I have never seen before in the several years I've been part of this community. Those users are the most qualified to judge your level. Don't be fooled by the term "Level Judges," and their pink names - they're a remnant from the original forums so their word isn't gospel. Some users that you should look for that have made incredible levels and are worth talking to about level design: Enjl, Marina, zlakergirl357, Darkonius64, Chad, Ace, and Bomber57. In general anyone who has made it to the final tiers of the Community Contests or won, is a good source but I know these people in particular and I have seen what they can do in their projects and levels.
Questions? Comments? Post 'em.