This is not the whole guide. The guide in the link provided explains several terms in crituiqing but I found this portion of the guide VERY useful below.
It's a long read, but worth it.
Credits go to Mavyrk from deviantART.
ETIQUETTE AND TIPS
This is a general list of etiquette and tips with regards to critiquing. Now that you have a good handle on the technical knowledge of critiquing, it's wise to get a handle on how to go about the act of critiquing itself; and, moreover, the act of critiquing on deviantART. These are in no particular order, and are just general guidelines, not rules.
1. Do not create a critique consisting entirely of what is wrong with a piece. A critique is an analysis of the varying parts of what makes art. Some things will be wrong, some things will be right, but you must remember at all times that a critique is subjective, and the people you're talking to are human beings. It is not a forum for bashing people you don't like.
2. Start out with a compliment. This will allow the person whose art you are critiquing to relax and accept your help. If you can, add in some banter. A conversational (or friendly) attitude will help you to be better received.
3. Understand that some people will choose not to accept your help or, heaven forbid, accept someone else's help. If you leave a critique and they respond with "Thank you, I will consider it", don't check back five weeks later expecting all your changes to be implemented, much less attack people for not implementing your suggestions.
This doesn't mean they do not respect your opinion, or that they feel you were wrong, but people sometimes disagree on matters of art.
4. If you absolutely detest any given art form, don't critique it. Leave your bias against anime, poetry, or whatever it is you dislike out of your critiques, and just analyze it for what it is.
Likewise, don't critique the subject matter; critique how the artist brings out the subject matter. If you're sick of angsty poetry, don't critique the artist on writing angsty poetry, critique them on how well they write the angst. Critiquing is not a forum for challenging the validity of someone's art form as art. There is nothing wrong with not saying anything.
5. Do not use 'bad' qualifiers ("This sucks", "That's bad") without offering to help the artist. That's not to say you have to step on eggshells. You may, at your choice, be brutally blunt, but you should be offering tips on how to improve.
6. In counter-point, don't make fluff critiques. It's very easy to pad someone's ego with a delightful little comment (not critique), but don't throw in some analytical jargon to make it appear more sincere than it is. Honesty, while wounding at times, is the best way to help the person you're critiquing, and why critique if not to help?
This doesn't mean that you shouldn't wantonly praise people if you want to. Just be honest about it.
7. Leave an interpretation of what you feel the artist is trying to convey, if it's not self-evident. This will help the artist tie in all of what you're saying in your critique. If they can understand where you're coming from, it may help them better correct their flaws, or accentuate their positives.
8. Make sure you not only view deviations in full view, but that you read any comments or peripheral information and art that applies. This will help you not only give you a critique that is in context, but it may also answer any confusion you have on certain parts of the art.
9. If you can't find anything negative about the piece, it's perfectly alright to leave a critique that just analyzes the positive. Remember, a critique is an analysis of the elements of a piece of art, and if you find that in analyzing a piece of art you can't find anything wrong with it, don't feel bad about just leaving a critique on the good elements. Maybe the artist was feeling a bit iffy on leaving in a portion of the art, and your positive analysis of that portion persuades him to leave it alone?
10. You're not critiquing the artist, you're critiquing the art. Don't fill the critique with comments about the artist (including but not limited to age, religion, political stances, etc.) and don't compare pieces of art by the same artist unless it is to illustrate some technique that you felt was better exercised elsewhere.
11. Proofread your critiques. The purpose of a critique is to be helpful, and most artists will not read an illegible block of text, which does little to help them in the long run if they never read your analysis.
12. Be genuine. Don't begrudgingly give them tips of the trade, and give them service with a smile. If you have a question, it doesn't do any harm to go ahead and ask them. It shows you have an interest in not only the art, but also the artist themselves, and will make you better received in general.
13. Leave jealousy at the door. This may seem like common sense, but all too often a person will tear apart a piece of art analytically merely because of some peripheral emotion, whether it be jealousy or anger.
14. Keep the fun factor alive. There are as many, if not more, hobby drawers and kids in junior high as there are college graduates and professional designers. There's no need to give a professional and superbly analytical critique to someone that is most obviously drawing for fun. That's not to say you can't help them improve, but you may not need to go to such great lengths to assist them as you might someone who makes a living from art.
15. Phrase your suggestions as, well, suggestions. "Perhaps if you..." and "Maybe you should try..." go over a lot better than "You need to" and "Go and do this."
16. It may be wise to segment (perhaps in paragraphs) your critique into different areas; one for analysis, questions, non-analytical comments, interpretation, and likewise. This adds to readability, which lends to the affect of the critique in general.
17. Please don't overlook the concept of titles. Very rarely do people critique on how the title of a piece applies to it, but it's a very creative outlet, and many artists put a lot of thought into them.
18. Remember the platitude, "If you can't say anything nice, don't say anything at all." To critique is to help, and no help comes from a brutal attack on a piece of art. On top of that, most people will ignore the advice of someone who appears to be attacking them, so even if there are valid suggestions within, it falls on deaf ears half the time.
Leaving someone bruised and abused does little to make them want to create more art, and if they don't want to create more art, anything they may learn from you is moot.
