Keeping it constructive: A guide to army list rating.
Note: This guide assumes that the maker of the list you are reviewing is male. If by some strange anomaly they are female consult my other guide Warhammer The Romantic Game of Fantasy Battles.
Try to not speak to speak in definitive terms.
Your list will get owned by X or Halberdiers are never worth their points
Use 'I' when stating things that you have found. Use 'others' when talking about what others think.
I find that two scroll caddies is often overkill - other people have tried X and been successful
Don't compare how the army will do against hypothetical armies. Or rock hard lists (Unless they have specifically stated that they WILL be facing rock hard lists like in a GT)
You're screwed if your opponent takes 3 mortars - This army would get owned by the Skaven army of doom
Questions to ask while looking at the list:
What level are they planning on playing at?
I think that the first thing you should do is to determine what level of competitiveness they plan on playing at. I like to sort the levels into three categories: new player, casual, and competitive. With new players be gentle and concentrate on making the list legal and the units effective at what he wants them to do. Don't reinforce the belief that a hard army list is necessary to win and let them try out fun magic items and gizmos while making sure that they aren't expecting too much from them.
Is he breaking any rules?
Does his free company detachment have light armour? Is he expecting to get four attacks with a Runefang by giving his GoTE an extra hand weapon? Correct him, and if something seems fishy, but you can't put your finger on it, summon the rules god by making a ludicrous claim about fast cavalry being able to reform then charge.
Has he expressed any unrealistic expectations for a unit?
Is he taking a single HLR and calling it an unbeatable magic defence? Give him a gentle dose of reality and show him how it's possible to use HLRs as part of a magic defence.
Are the units efficient at their intended job?
Don't change the purpose of the unit. Make the unit better at its purpose. Suggest giving those hammer knights a war banner instead of an extra rank.
Is his list seriously missing any components?
Here is where you get to guide him towards using all those points you saved him by pointing out the limitations of the Banner of Valour. If you want him to see the value of 'nilla knights suggest he adds them here. If he could use a scroll caddie, now is the time to show him how he could add one. Just remember not to go overboard and to keep the heart of the list intact.
Finally ask yourself:
DO I KNOW WHAT I'M TALKING ABOUT?
If you answer no here, will there really be any benefit aside from increasing your post count? As said above if you haven't tried it yourself, or you are using others' advice, admit it.
Disclaimer: In no way is this guide intended to be offensive to the French or any other nationality. Please do flame me saying it is. Definitely do not put words into my mouth by assuming the guide is anti-French and supporting my correct stance. For the love of god don't get this article locked by being stupid. If you don't know what any of this is alluding to don't ask.
Feel free to add more or comment on points.