I've been playing The Binding of Isaac loads over the past weekend. Here are a few tips which I think might help you beat this short though somewhat merciless game. Perhaps these tips might even have you beat it in the next ten games. If this is the case, you'll have to let me know.
1. Go For The Upgrade First
I can't stress this tip enough. No matter what kind of player you think you are, your first objective should be to look for the room that contains the upgrade. Each dungeon has one; They're the rooms with a entrance that has a gold tinted doorframe.
Most of the upgrades will prove useful to you in your current game. Some will improve your overall stats, including range and speed. Other upgrades will take residence in your 'item' slot, often useable once every half a dozen rooms.
Ultimately you'll want to stock as many upgrades as you can, not only to help you with boss encounters, but also the biggest of them all: Mom.
2. Don't Be Afraid To Try New Things (Including Pills)
Your first dozen plays of Isaac will almost garuntee new upgrades to try. This is because the game has so many powerups it would be impossible to stock them all in one game. Because of this, some people might have a hard time remembering which powerup does what.
In the heat of the moment, some players might be tempted to try certain powerups anyway and this is certainly no bad thing. Though all upgrades have an affect on the overall game, and difficulty, it is up to the individual if, for example, they have to decide between Mr. Boom or Mom's Bra. Don't know what either of these do? You will, eventually. :)
It is true some powerups are in fact powerdowns, by which I mean a decrease in stats. Such powerdowns are often found in pills and all pills, no matter their appearence, are always a risk to take. Unlike general powerups, which are saved in the games 'collection' feature, pills are unique to each game. While it may be true 'good pills' and 'bad pills' are colour coded, this can be neither confirmed nor denied. What I will say is the good generally outweighs the bad. With this is mind, I would suggest you try everything the game has to offer and you might well be pleasantly surprised! (I do not recommend such 'pill popping' to take place in real life, though.)
3. Keep Moving
Your best strategy when maintaining your health is to keep moving. That your ability to shoot is not restricted to the movement keys is a good thing as this will allow you to 'circle strafe' around enemies which, at times, will become a little fire happy. There are exceptions to the rule, perhaps. For instance, there are bosses which can take up a third of the screen but even these can be dealt with with the circle strafe rule albiet with a hint of modification.
With a higher number of enemies, the game can suffer from a bit of slowdown. My advice would be to use this to your advantage. Just because the game runs slower doesn't mean it gets easier, though. You still need to keep moving, no matter what. The faster you move, the harder you will be to hit.
4. The Enviroment Is Your Friend
Those who are looking for extra goodies (and why wouldn't you be?) would do well to distinguish fires and destroy piles of dung as both of these have a remote chance of hiding a collectible. Additional to this is the rare discoloured rock which, if blown up, will shatter to reveal an arguably more valuable collectible such as armour hearts or a treasure chest containing something more.
The enviroment can also work for Isaac when he is encountered by enemies. Most enemies in Isaac are vulnerable to fire and beds of spikes. Enemies which have preference to follow the player (such as zombies) are perhaps the most 'at risk' of fire and spikes if the player is nimble and accurate enough. For instance, in later levels, groups of zombies can be lured toward beds of spikes if one adopts the 'circle strafe' strategy.
5. Accept Defeat
Despite its minimal length, The Binding of Isaac is a hard game. For all its randomness, sometimes it is not lack of experience which is to blame for one's defeat, but rather an unfortunate case of bad luck. Sometimes the game will starve you of extra health. Soemtimes the game will throw tons and tons of enemies your way. Sometimes you will choose to use a powerup which will end your game right there and then. Some of it will piss you off, but all of it is there to inspire humour, including humour of the 'gotcha' variety.
Don't take Isaac too seriously. Remember: If at first you don't succeed, try and try again. Besides, it's the trying and trying again which makes it fun.