There’s a general opinion that judges’ work is very difficult to do. That it takes careful study of rule books, participation at week long seminars, and years of intensive practise. Though there’s hardly any indication that these requirements have any merit. These statements are usually made by people who overestimate their skills. Everybody can be a judge. If you consider to become a judge don’t hesitate to start scoring right next weekend.  
Of course for an aspiring judge it might be helpful if you know what a control line model is, that in most cases it is safely tied to some wires, and that it usually tends to fly in circles. Ignoring this might find you within the so called flight circle with less than pleasant results. Another requirement is the knowledge that a control line airplane can do crazy manoeuvres, vaguely resembling those geometric shapes long forgotten since school lessons. Add to this a sound self conceit and at least some modest eyesight - and there’s nothing that could keep you from judging at the Nats.
The most important thing to call for is a comfortable armchair . An organizer who cannot supply this surely lacks some finesse, and you should penalize him by offering your help but not appearing at the planned date. Providing some delicate meals and refreshing drinks is necessary if a judge is expected to score a little more than the warm up flight. A short mention of paid expenses should be enough to cause the organizer to react accordingly.
There’s no need to study rules. They are too complicated, leave no room for interpretation, and are too difficult to find in the rule book anyway. You should leave this to the pedants . Don’t waste your time listening to boring speakers at judging seminars. They try to tell you what they don’t know themselves, deny your personal right to interpret the rules, reduce and confuse your already limited knowledge even more, and try to destroy your self-confidence. Simply refuse to take part in these discussions - they will just raise your competence to an average level, and that’s what you should try to avoid at all costs.
. Judges guides are a perfect means to guide people - do you really mean you want to be guided? Without the freedom of decision your personality will fade away point after point, which is pointless . Develop you own view of how a manoeuvre should look like, how it has to be flown, what the airplane should look like, and what kind of wardrobe the pilot should use when he dares to present his flight to your eyes ( he may change it for the other circle with other judges ).  
  There’s no reason to agree with the head judge. After all he is a bureaucrat who exactly knows the rules, but definitely lacks imagination of what wonderful manoeuvres are possible in strong wind. Some pilot’s presentation may differ from what you’d expect to see and produce some funny shapes. Especially beginners have a creative talent to mix rounds and corners into an exciting flight path. This cannot confuse you. You simply enjoy the presentation. Make your feelings known and don’t try to suppress a freeing laughter.  
. If you have missed several manoeuvres while enjoying a drink, don’t shy away from having a look into your neighbour’s score sheet. You’ll be surprised at which and how many manoeuvres he has missed. Probably you can exchange informations.  
  On international contests your reputation as a respectable judge will greatly improve if you try to consider the cultural differences of pilots from different nations. Germans, for instance, will instantly complain if you present him with slightly more than the correct amount of points, and if you don’t add those tiny manoeuvre drawings ( including all errors ) onto the score sheet. American pilots are much easier to handle. Just make favourable remarks about the stunning finish of their airplanes and they will rate you the most generous judge in the world ( even if you are not American ). Japanese pilots will gladly accept the worst thinkable score if you perform several respectful bows as deep as your spine permits, before and after their flights - and they will smile.
All judges are nice people. All pilots will confirm this. Many a deep friendship has started as a respectful flyer/ judge connection. You can easily further this wonderful situation. Always have business cards ready to hand out among the pilots. It would be immodest to forget the numbers of your bank account. However resist the temptation to include your home address. Many pilots are not quite happy with the numbers you’ve written on their score sheet. Some of them like to make strong objections and have a habit of raising the decibel level of their arguments if you do not agree. Don’t worry ! Just remind them very politely that you will be a judge at the next contest which they intend to participate at.
  Don’t be surprised if you find out that at all contests the weather is so foggy that you cannot detect the models at the far side of the circle. Your doctor will confirm you that your eyesight is only partly limited and you need not fear total blindness soon. Not all is lost as long as you can precisely spot that attractive blonde passing close by. Sun glasses are a big help to hide your direction of view.
Between rounds take a close look at the scoreboard. Criticize the scores and tell your favourite pilot what fancy manoeuvres he should include to improve his score. After the contest write a rule proposal, declare that most rules are unnecessary and should be deleted, and explain to the last detail what you want the rules should look like. Finally accuse the rule makers in charge for being biased and not cooperative.
All such conduct will quickly and easily make you a most welcome and highly respected character at any contest circle.

PS. After desperately trying to do judges work for the first time at a local beginner contest I consider the above given dissertation not 100% correct in a few details.