what is the most effective way for a ~2100 player to improve for tournament play?

thanks

"the most effective way" would depend on the player's present deficiencies.  btw, If cost were no objection, you could subscribe to this site's "premium" services, which include training aides such as 'Chess Mentor'.  I think when subscribing, there's a:  10-day free trial, and a policy of a 30-day one-time money back guarantee, which would take much of the risk out of testing the site's paid offerings.

There are tons of potential deficiencies that you might care to address, ranging from your playing ability (you're approaching Master level, so more attention to openings might prove prudent), to general health (aerobic health boosts our brainpower and sharpness; a good diet avoids roller coaster mood swings that can be majorly distracting, etc. etc.).

My suggestion:  play masters, and ask them where they believe your game is deficient.  The site's just started developing a new training program that may prove helpful at your level after a few months of refinements.  See http://www.chess.com/article/view/study-plan-for-beginners-bringing-it-all-together2 and similar blogs by 'webmaster'.

sftac

I don't think there's such a thing as a generic "2100 Player." At that level, every player has his/her own set of strengths and weaknesses. Obviously, it's always be better to improve your tactical play, end game knowledge, etc., but you have to be able to look at your own game and be brutally honest about indentifying your weaknesses--or you need to get a coach to do that for you. But a good coach will tell you things you don't want to hear!

Do you mean 2100 chess.com or 2100 OTB?

There are very different answers to each

There is a big difference between a 2100 turn based rating and a 2100 live rating. First get rated by playing some live games, so you know where you are at. Then we can suggest improvements from there once we know your strength.

OK, i meant 2100 correspondance, and cost is sort of a problem

You learn more from your mistakes and losses than your victories.  I urge you to review an occasional loss, especially those where you're just not sure where you went wrong.  Do this from time to time, and it ought to help you avoid 'repeating history' (making the same mysterious slips again and again).

sftac

ps.  Try not to make moves when you're tired.  Pick times when you're feeling fresh and relaxed.

Whatever you dread to study the most is generally what you should study. It's a very simple solution, yet so difficult to execute.

Going over your games, especially losses, still is probably the best way to learn. You have to do it right though. Focus on two key things:

1.New patterns you obtain from comparing your moves to the computer suggestions;

2. All of the errors in your thinking you can contemplate (too defensive, being afraid of a move due to erroneous reasoning, attacking too quickly, literally anything -- it should be made obvious to you as you go over it).

Be as objective about your weaknesses as possible whilst trying to tighten them up constantly. If you know certain endgames well (like rook and pawn endgames) for example, you won't get nervous when you go into one and have to convert your extra pawn. Sometimes the only way you can convert an advantage is in a favorable simplified position!