I've taken a few months off from playing but I'm thinking about getting back into this game. Here is an old guide I wrote to the SC2 general forums back in September. It appears as if blizzard doesn't allow google to index their forums so, for the sake of newcomers searching for strategies, I'll post it here:
I thought i'd share to the community how I (a mediocre player) cheesed his way into the Diamond league. I have beaten many a diamond league foe and I believe everyone has the ability to hit diamond so long as they practice and stick to tried and true strategies that work.
I'm by no means an RTS god. When I picked up the game I hadn't played an RTS since 2004 and I initially placed in Silver league. I've viewed my own replays and my APM is ~ 50 which is average and a far cry from the pros who have APM 100+. As I worked my way through the leagues I discovered strategies which generally worked against a certain caliber of player and a certain race.
I believe that provided you have a basic understanding of RTS fundamentals and Starcraft 2 you can be Diamond too. As terran here are the strategies that got me to Diamond. I'm sharing with you the gameplan that I used in virtually EVERY matchup.
TERRAN STRATEGIES FOR REACHING DIAMOND
1) TERRAN VS PROTOSS
My basic strategy vs Protoss even to this day (in Diamond) is to simply mass marines and attack at about the 7 minute mark which typically also corresponds to ~60 supply assuming you have 3 SCV on gas and 16 minerals and the rest on marines.
There are many variants of MM but the variant that I prefer is 3 barracks each with a reactor and pumping straight marines. Typically I don't even upgrade my marines. I just push in early with an overwhelming number. Get reactors up ASAP so you can get as many marines as possible for the 7 minute push! It's very important to attack soon and attack before protoss can obtain units that hard counter your marines: high templars, collosus
ACTION PLAN: Use Mass marines vs Protoss and make sure you attack at the ~7 minute mark. Scan their base before to see what they have. This will work wonders in Platinum or below and work reasonably well in diamond as well.
2) TERRAN VS ZERG
In the lower leagues (Bronze, silver, gold) most Zerg don't know how to effectively use or micro banelings. It seems most in these leagues don't go banelings at all and if they do they either don't have enough or micro them extremely poorly.
ACTION PLAN VS LOWER LEAGUE ZERG: Take advantage of the incompetence of lower league Zerg opponents and go MASS marines. Scan their base and check for banelings next. IF they don't have one, then you can safely mass more units in your base until you think you have the advantage. Other than banelings the only units they have which hard counter marines are broodlords or maybe infestors. But both of those units will come much later. You should have the win long before that. Go for mass marines and you will win most of your matchups vs lower league zerg.
ACTION PLAN VS PLATINUM ZERG: Most platinum zerg I find will indeed go banelings. Sometimes you can out macro them and just pump out too many marines for them to handle but it's a toss up. Typically vs Zerg in Platinum I like to push quick with seige tanks supported by marines. I go 3 rax (no reactor or tech lab initially) 13 gas (saturated once done) 1 factory. Try to get the factory out ASAP and get seige tech researched immediately. Once you have 2 tanks you should have a decent quantity of marines fromt the 3 rax. Push in with your 2 tanks and your marines. It usually is too much for them to handle so early. I also find that in platinum zerg start going fast expand. So this build will really hit them hard and punish them for expanding so early.
Interestingly, my preferred TvT strategy was nerfed by Blizzard. A supply depot is now required to build a barracks, ending BBS builds which have existed since SC1... I'm kind of disappointed that they had to resort to such an extreme measure..
Hoped this helped!