I will start by saying that I'm not a pro at Dota 2. I still do stupid mistakes and lose matches all the time. This is not an article about how to be a perfect Dota 2 player but hopefully by following and put the following tips into play you might find more successes in your match and can say 'GG' proudly!
These are some of the tips I muster from years of playing DotA & now +Dota-two :
1. Try to have a balanced team. A balanced team has minimal 1 of the following: tanker, carry, and disabler. These 3 are the most important roles in my opinion. Other roles such as nuker and support are not very vital but would make a great addition to your team.
2. Courier. Traveling back to base on foot/portal wastes time and money. Have courier transports your item while you keep farming the creeps for more money and EXPs.
3. Choosing items. For beginners, you can always follow the recommended item lists. And after you gain more experiences, you can experiment with different item builds for your favorite hero.
4. Choosing lane. Mid is better suited for pusher, carry, and ranged. If you're playing as the Radiant, stick to bottom lane and as Dire the top lane if you prefer to hug the tower. Tower offers extra protection from ganks and helps you farm the creeps!
5. Choosing partner. 2 carry in a lane is bad. You both need to feed asap and by staying in the same lane both of you will conflict with each other, and won't be able to feed optimally. Possible preferred combos: carry + support, carry + disabler, tanker + nuker, tanker + carry
6. Choosing skills. It is always tempting to pick the skills that give you maximum burst damage, but unless you have a big mana pool or the skill consumes small mana, you need to consider the mana costs. For the first skill I usually pick skills that disable the enemies (if I'm partnered with a nuker or a carry so he/she can finishes enemy heroes) or skills that boost my atk damage (if I'm mid, to harass enemy hero). For the second, you can pick passive skills or skills that offer protection if you are laning against harasser. For the next subsequent levels, pick the skills in accordance with your mana growth and your role in the team (are you a ganker, harasser, carry? Do your team have no disabler except you? Drow keeps on harassing your ally? You get the idea).
7. Using skills. it is not recommended to spam your skills like crazy every time you get the chance. You won't have enough mana when the chance comes for a kill. Keep an eye on the mana costs of your skills and enemy heroes' remaining HP. Also communicate with your partner if you decide to go for a kill.
One example is when I'm using Chaos Knight, partner with Lina. I note that the total mana needed for my 2 skills (Chaos Bolt, Reality Rift) are 210 mana. I let the enemy heroes push to my tower, let's say it's Drow. Once she gets close enough I signals my partner to concentrate attack on Drow. I launched Reality Rift to pull Drow even closer to our tower, her HP will deplete quickly by the attacks from tower and Lina's attacks/spells. I then launched Chaos Bolt as she tries to run while Lina nukes for finisher. GG!
8. Using wards. There are 2 kinds of ward. Both with different functionality. Use Sentry Ward to reveal the annoying Stealth Assassin, Clinkz, Bounty Hunter, etcs with stealth ability. You can even put it on lane. Unexpecting SA might thought he was invisible while we prepare for the all-out gank on him lol.
Observer Ward should be placed on vital locations (river, jungle) to observe (duh) enemy's movements. This way you can anticipate enemy ganks or move in to gank on the lone hero travelling through the river.
9. Scouting. Some heroes are tailored for these purposes (Bounty Hunter, Clinkz, SA, etc). They can turn invisible, making them very safe to scout enemy in the jungle or tracking enemy hero to be killed next. If you play as 1 of this hero, always scout to give better edge for your team. Watch out for wards though.
10. Pushing. You can't win by keep killing enemy heroes but you CAN win by destroying all enemy towers. Carry and pusher are the best roles for this purpose. You need to reassess the situation if enemy heroes keep dying but all their towers are still left intact but you've lost some of yours.
11. Ganking. Ganking is when you and you team decide to kill enemy hero/s, usually on more unfair circumstances such as 2-to-1, 3-to-1, 4-to-2, etc. While ganking look out for the chance of enemy ganks themselves. For optimal gank, you will need disabler (STUN!, slow, silence, trapper) and carry. You can start to gank once you reach level 6 and gain access to your ultimate skill.
12. Ending the game. Don't ever delay or prolong the matches, even if your team is at an advantage. By prolonging the match, enemy teams will get the chance to feed and if they happen to get fat (fed enough to buy crazy items) there is a chance the situation will turn around. Push, gank, end the match quick and don't let enemies gain advantage!