For a rule that many people seem is a given, the infamous double melee lane is a phenomenon that is anything but extinct in lower level play. To a veteran player, the implications are clear: not having at least one ranged hero in the lane is a one way ticket to not getting any last hits, any denies, and in many cases, any experience. When sitting in the hero selection screen, it helps to count all melee heroes picked or prepicked. If the number is three, then you must make sure that one of them is headed for the middle lane. If the number is larger than three, something needs to be changed.
The Laning Phase's importance to the game depends how long the game goes on. In most cases, however, games rarely exceed 60 minutes, making the laning phase extremely important. The error that many players make is that they rely too much on the hero in the middle lane to assist them in ganking. While it is true that the middle hero should collect runes and gank the lanes whenever possible, many heroes that run the middle lane are simply not able to find the time to gank all the time. Often players won't take this into account and expect the player in the middle lane to solve all their problems. In reality, however, much of the blame can be put in the lane that failed. Players who are new to the game will find it difficult to harass and initiate local ganks in the lane. Harassing, pulling, initiating and 'AI-pulling' (right clicking an enemy hero and then running back to pull the creepwave back towards you) are all extremely important things to learn and apply in the laning phase. Learning when to initiate within the lane requires communication and timing, which, while I wish I could sum up in a few sentences, requires practice more than anything to master.
Although the term might seem crude, dicking around is a very serious issue which plagues lower level play. It helps to think of every creep in the lane as potential experience and money. When nobody occupies a lane, this experience and money is essentially being thrown into the trash. More times than I can count have I seen lower level players perplexed at how the enemy heroes have accumulated so much experience and so many items. Simply put: they spend more time in the lane and less time between lanes. Of course, depending on what kind of hero you are playing, being between the lanes might work to your advantage. Running between the lanes when it doesn't benefit you, however, is something else. As the famous saying goes, "time is money" and every second you spend treading between lanes is money lost.
Tying into point number 5, the correct hero composition is the key to any game's success. Contrary to popular belief, a good hero composition can make a large difference in any tier of play. When I started playing DotA a long time ago, my friends would often make some sweeping generalizations when trying to define roles and compositions, and I would often hear stuff like "we need more stuns". As time went on, however, I realized that although it's important to get a diverse group of hero roles on your team, "Stuns" are somewhat of a miracle mechanic. Any ability that stuns you also immobilizes, silences, disarms and perplexes you, a mixture of disable which often goes under-appreciated. The point I'm trying to make here is that in addition to getting a diverse mixture of roles (friendly reminder that "Tank" is not a role) and a lineup that doesn't have a double melee lane, one should always count the amount of easy to land/area of effect stuns your team has. Additionally, you should also think about what two heroes will lane together, but that's a story for another time.
The easiest way to lose any HoN game, of course, is to not buy a courier and wards at level one. For any higher level game, this goes without saying, but for lower level play, it remains an issue forever unsolved. Wards and a Courier at level one are, in fact, the most crucial building blocks to winning any game. The chain reaction which ensues when this criteria is not met often goes unnoticed. Without a courier, the middle lane cannot send a Bottle (friendly reminder that you should never buy a Bottle at level one), without Wards the middle lane cannot compete for runes. Without runes, the middle lane cannot fill his bottle, and without a filled bottle the middle lane cannot gank the sidelanes. Without ganks to the sidelanes, the sidelanes are susceptible to failure (not to mention the middle lane which is basically guaranteed to fail). Like the Keel of a boat, without Wards and a Courier straight out of the gate, your ship is destined to sink. The tragic aspect of this is, as already stated, that the connection between the cause and effect often go unnoticed and the hero in mid is often given the blame.
You may notice that most of the things I have listed all stem from decisions made at the beginning of the game. The hard truth about Heroes of Newerth is that you can often (and very easily) dig your own grave before you even kill your first creep. Without the right hero composition, you will lack proper lanes and proper Support. Without proper Support, you will have players who feel no obligation to buy Wards of a Courier and lanes that are destined to fail. Without these things, games simply cannot be won in a game of equally matched skill.