How do you think about the game and your moves? How many moves ahead do you think about? How many possibilities do you have to consider? Do you think more about your opponent’s history or their possibilities?
It’s really hard. Grandmasters are very good. I’m only going to speak to my “classical” tournament games (6 hour time control) games versus Grandmasters. I’ve been fortunate enough to have many of these games, including 4 draws with Grandmasters in classical tournament games (GM Roland Schmaltz, US Open Framingham 2001; GM Yona Kosashvili, Curacao 2002; GM Ildar Ibragimov, Parsippany 2004; GM Arthur Bisguier, Foxwoods 2004).
- Remember that GMs are (almost) impossible to prepare for. They’ve all played hundreds of openings. Just find what they are most likely to play and make sure you have something in mind for each. Remember that GMs don’t generally like to play their “best stuff” versus lower-rated players. You’ll get something a little weird in all probability.
- Know your openings cold. I cannot stress this enough.The four games I drew were in lines I knew very very well (Sicilian Boleslavskij, Sicilian Grand Prix, Closed Ruy Lopez and Leningrad Dutch). This meant that I was in a situation where I understood the plans, didn’t take up oodles of time in the opening, and gave myself the best position possible. Games I lost (most especially GM Gildardo Garcia, New York Open 2000; GM Alonso Zapata, Curacao 2002; GM Giorgi Kacheishvili, Foxwoods 2004), were games I didn’t know the openings as well. The last thing you want to do is find yourself where you are in a) a worse position b) with less time c) against a better player. You’re toast in those situations.
- Trust yourself. If you can’t figure out the flaw in a line, go for it. Don’t ever start second-guessing yourself or seeing ghosts. Remember, you have to play chess the best way you know how. The last thing you want to do is change your openings/thought process/habits for a game against a strong player.
- Relax. They’re a GM, they’re supposed to beat you! Feel free to fire uppercuts and play the most important openings to your repertoire. If you have an opportunity to put pressure on your opponent, do it! This is a great learning opportunity for you, don’t waste it.
- Don’t get freaked out by the spectators. This is one thing that happens in games you play versus GMs that doesn’t happen in your “normal” games. Everyone in the tournament is going to glance, or even worse, spend time looking at your game. When I played Kosashvili in the first round of Curacao 2002, at one point, I had GMs Kortchnoi, Timman, Zapata, Macieja, Benko and Averbakh staring at my game all talking to each other (this was after we repeated moves once). That can really mess with your head. (Fun aside, after drawing Kosashvili, who was one of the favorites and eventually tied for first, tons of people came up to congratulate me. Kortchnoi came over, said “You made a draw?”, and at my head nod, he thought, and said “But you are White, what is achievement?” Life is tough at those levels.)
- Be professional. No clock banging, no over-adjusting of pieces, no draw offers, etc. Learn something. Sit at the board the entire time. Focus. You can talk to friends later. Remember Ivanchuk’s famous quote “How does it feel to play?”, just enjoy it.
As far as the rest of your questions, sometimes I’d calculate some lines very deeply. Other times, I generally went on intuition. I usually felt “more” focused during GM games, but not significantly more. I honestly didn’t do anything different. It was just chess, versus someone who is VERY good at it.
By the way, I approach simul games the same way, and have been very successful in Simuls (draws vs. Anand and Bareev most notably). Just use it as an opportunity to play your best chess and see how you match up. If you’re any good, you might nick a half point (or even more!) and be a hero. If not, you had a fun battle.