Pitch like you might in real life, or what you'd recommend a pitcher do in an MLB game that you watch on TV.
Pitching in MVP, is by far the most realistic of any video game I've ever played. As you play the game more, you will see that each hitter will pick up on your patterns. You should be playing with hitter's eye on as a batter, so you'll be able to see this when you hit, but look at the pitch history with each batter. The game will pick up on many patterns that you as a pitcher can do, and if you're playing on All-Star or MVP, will really punish you for...such as:
-Always throwing strikes. Waste a pitch outside the zone to try and get them to chase every once in a while, especially if you're ahead in the count.
-Only throwing a particular pitch in a particular location (IE if all your sliders are outside to righty batters, they will pick up on this, take the ones that are balls, and hit the ones that are strikes better).
-Always throwing a particular speed first pitch (if you throw first pitch fastballs to everyone, they'll start to get hit)
-Generally favoring a particular location to that batter with your pitching. While you usually want to avoid hot zones, it's good to come in there every once in a while to keep them off balance.
-Always going for corners. It's good to aim outside middle or inside middle every once in a while. High center and low center and riskier pitches, just as in real life, so these locations aren't recommended unless you're going out of the strike zone to get the batter chase.
-Following a pattern. If every inside pitch is followed by an outside pitch, or vice versa, hitters will pick up on it. Every so often you'll want to double up on them in a particular hitting zone to keep them off balance.
In addition to this, you'll also see the hitter will occasionally "cheat" inside or outside on a particular pitch (his hot and cold zones will move as you begin your pitching motion). This is another example of this at work.
Also, you always want to put full "juice" on every pitch. It's not how hard you throw that the "power meter" measures, it's how effective the pitch is. So a changeup with "full power" will not actually be faster than one with, say half power. With breaking balls, it controls the break of the pitch. You always want to pitch as close to full effectiveness as possible...the only exception to this is if your pitcher is becoming tired, then you may have to take a little off in order to hit the green.
In higher difficulty modes like All-Star and MVP, the meter is also more sensitive. If you hit the yellow areas "Early" and "Late" immediately surrounding the green, it can actually be used to aid the effectiveness of your pitch. It's hard to explain this, but I'll try. If you are a righty pitcher facing a righty batter, and you try and throw a breaking ball DOWN, AWAY, or DOWN AND AWAY from a righty batter, missing "early" will cause the pitch to miss closer to the plate, while missing "late" will cause the pitch to miss further away from the plate. As long as you're in the yellow area, however, the pitch will not register as a "mistake" and telegraph location to the batter, but it will physically slightly miss where you aimed. You can use this to your advantage. If you want the hitter to chase, aim way out of the zone, and miss early. If the pitch is just below the zone, and you miss early, the hitter may well hit the ball (possibly even for a hit), so in that case you want to miss late. While it's easy to say you always want to hit dead center of green, sometimes the hitter won't chase if you do, so play around with this and get them to chase out of the strike zone with it. You can also use it with pitches that break opposite, such as the screwball or 2 seam fastball. In those instances, what I said also applies to pitches UP, IN, or UP AND IN but is opposite...here, missing early will cause the pitch to miss further in off the plate (or up), and missing late wil cause the pitch to miss closer to the plate. With 2 seamers in particular, this can be used to your advantage. Aiming inside off the plate and missing "late" can sometimes cause the pitch to stay on the inside edge of the plate for a called third strike.
The pitching reality is one of the reasons I love this game so much. And the hitting realism too (since walks are appropriately common, whereas other games it's much too difficult to walk). The only two things I wish were different are give pitchers up to 6 pitches, and allow pitchers to designate pitches as primary/secondary/tertiary so hitting against certain pitchers feels more realistic (IE facing Randy Johnson you'd expect more FB/slider and less splitter). Also it's very difficult to strike guys out with knuckleballs (the pitch) and changeups in the game, that should be a bit easier as well, and fastballs could result in more fouls to compensate. But I digress. MVP 05 is still the best.