Some guides end up giving you 10,000 points to focus on and leave you with no real sense of direction, because in the end you've basically been told to work on everything. This guide will feature 5 main points, not all of which pertain directly to gameplay itself. Some of these tips are unorthodox or seem unimportant, but trust me they work and will rank you up quickly ಠ_ಠ
TIPS (5 of them)
1: This is easier to demonstrate with pictures(see below), but please always, always, always, aim for the fucking head. If you're a DMG or abouts, you probably know this quite well. Nonetheless this tip could apply to you. THERE ARE 3 GOOD REASONS TO AIM AT HEAD LEVEL AT ALL TIMES, two of which most players probably don't think about, but I have found to be certainly true.
One (obvious reason): It better prepares you for the unexpected or expected enemy in a firefight. If you aim at head level at all times, there's a good chance that first shot will end them then and there. Taking the time to line up the shot because you decided to run around with your gun pointing at the floor will get you no kills fast.
Two: Better focus, lower reaction times. CS is a game that rewards the focused and ready gamer who is able to react quickly. When you run around the map only really focusing on the WASD movement of your character, you subconsciously and unintentionally lose a level of interest in the game. By constantly ensuring your crosshair is at head level, you make sure all of your brain is focused on the game, both the WASD component, and the mouse/reaction component. This helps fight game fatigue as well, as counter-intuitive as it might seem. Players in the later rounds of a match sometimes fall off because they lose interest and focus on the match, running through the paces without actually keeping a dynamic interest. By constantly keeping your crosshair at head level, more of you is focused on the game, thereby lowering your reaction times and making you a better player. This reaction time effect is twofold, one part being your crosshair is already in the right position, the other being your brain is more focused and ready to react. The end result is a shorter time from vision to trigger pulling.
Three: You develop a better sense of crosshair motion and speed. This one is simple but again overlooked. If you spent the first 30 seconds of the round constantly adjusting the crosshair to be at head level, your muscle memory is going to be much more accurate when the moment of glory arrives. The players who moves the mouse 5 times to get to their spot, vs the 100 micro-movements of the focused player will end in the first guy dying more often than not. Crosshair placement in battle has a lot to do with muscle memory, so the more pre-battle placement you do, the more likely it is to be accurate in your firefight.
Picture examples Remember, doesn't matter if you're running, walking or still in these pictures the same principle applies: YES  NO  ***** YES  NO  ***** YES  NO  ***** YES  NO 
2: Do not freaking peek, or defend aggressively. Hurr durr Gu2014 I know that idiot you say. My definition of peeking is more extreme than a lot of players. By that I mean, if you're exposing yourself even a little in a situation you don't need to, that's peeking. Like all these tips, the following will be a specific example of a general mindset you should try and adopt.
NO  NO  NO  NO 
YES  YES  YES 
In my experience you'll end up winning far more engagements this way, and prevent lucky one shot dome blasts that make you want to uninstall. Remember, the idea is to never be anywhere they might traditionally expect your head to be. That is the easiest way to die. This mindset boils down to, be the reactioner, not the reactionee. You want to be the first one to react and pull the trigger, not the second. This concept alone might be the most powerful rank boosting method available. Sitting in common spots, where the enemy will peek you and likely shoot first, is just a bad idea. Defending from uncommon spots where you have the drop on them, and likely shoot first (like in the pictures above) will win you more battles. Obviously sitting in the same places round after round will get you killed, so don't do that. Also, don't bait your team. If the team is pushing as a group, or the bombsite is being rushed, jump out and help your team. This is highly situational, so use your best judgement. Playing sneaky should never come before playing as a team member.
3: First to react mentality and playing in sneaky spots is also going to be highly dependent on a low ping, so tip #3 is short and simple. mm_dedicated_search_maxping 50
The above command in console will ensure you don't ever land in a competitive match with a ping higher than 50. With my style of play I get absolutely destroyed with a ping of 80 or more.
4: Use your grenades wisely and PLAY SLOW. This relates to the previous tips, but one major difference between high level and lower level players is aggression and timing. That round timer has 3 minutes on it, and in your head you shouldn't even think about getting ancy to take a bombsite until 40 or less. Obviously rushes and eco stacks will null this point, and when those happen you need to go as 5 and be as aggressive as possible. When the gun round comes though, patience will be your greatest ally. The biggest mistake that is easily fixable by players trying to rank up would be to simply stay put. If your team gets a few kills at ramp, don't just push lobby because it's 5v3. Just because you get 3 kills banana doesn't mean sprint down mid from A. The quickest way I turn around rounds just like that, is by waiting for the early pusher and evening the odds. Some players are even sillier by just pushing early for no reason. This is more true on CT side where you ought to be defending. Again unless your team is executing a coordinated rush, don't force anything until under a minute. Odds are someone will push you, and when that happens you will have the advantage.
As far as grenades go:
Don't use all 4 in the first 30 seconds
(More commonly) don't forget you have them and take 4 to your grave
In tense combat situations a lot of players seem to forget they even have them. Instead of using a smoke or flash to gain an advantage late in the round, they just go in guns blazing. CS round meta makes players forget this I think. The beginning of the round you throw nades and flashes in common spots, and afterwards use only your weapon. Grenades need to be a viable option in your mind all round long.
5: Use your words. You've heard this before, but communication wins games. I get highly specific in my callouts, noting an exact number, which direction they're going and what guns they have. It might not seem like much but there is a huge difference in the odds of your teammate living when you say: "some lower b" or "2 lower b pushing, looking at cat right now." The more specific you get, the better chance your teammate can capitalize. Each and every time you die, every bit of information you have should be relayed to your team. The most damaging teammates are those who say nothing when they die, and allow teammates to die because of a lack of information.