Hi,
since I'm kind of a lamer at Civ4 myself, I think I can give you some advice at eye level

.
Hi all. Despite losing GOTM 12, which was apparently really easy, I'm returning for more punishment and hopefully improvement on GOTM 13.
OK, first of all in my opinion GOTM12 was super-easy, so if you lost that one you will have a tough run with this one, since it's one level higher, on a large map and epic speed (which you might or might not be used to).
As this is only my 4th full game, I'd really like some broad, strategic advice. I'm wondering how you decide what victory to go for. Is it based on the start map position or a strategy that you're familier with? I'm thinking of going for the spaceship as this is the victory I know best.
I won most of the games I actually attempted, except for my first respective attempts at the next higher difficulty, and then it was mostly an early defeat/resign due to lack of military defense. So my first advice would be not to totally neglect your military in the beginning, even if you want to play a peaceful game. At least build some archers/axes to deal with the barbs and for fogbusting. Since this is a large map, there will be a lot of fogged area for most of the game, so you
will have barbs around. Don't lose early cities to them because you "needed that axeman somewhere else"

.
Go for the victory you feel most familiar with (Space in your case). Don't experiment without testing first on a higher difficulty than you are used to. Personally I think Cultural is pretty easy, since there are solid, easy to grasp "recipes" on how to achieve it. Also, if played properly, you will have won before the AI has any chance to complete the Space Ship, so you won't be racing with anyone of them. Now, if it turns out that we get an isolated start (i.e. not meeting many (or any) contenders before Astronomy), you would have to make sure that you can found three religions on your own because you won't get them from neighbours (for a good Cultural win you need religions).
Also, I'm planning to be more war-like than usual. In both test games I was next to Monty, who continually attacked me so I've got a lot better at warmongering. Maybe foolish, but I think I can challenge the AI best at battling, rather than city production.
It is kind of mandatory to show aggression on Monarch and higher levels. Be relentless, don't hesitate to build only military units for extended periods of times and whack your neighbours at the next best opportunity. I found myself to be quite a whimp regarding aggression, but then realized that it is not hard at all if you are consequent in your actions (ie. not flipping needlessly between teching/building/warring, instead sticking to one until your milestone is reached). I also think it is a lot easier to defeat one or two oppos as early as possible, since they expand faster than you do and cause you a lot of grief later, when they will have more land/cities and possibly are ahead in tech. So try to get copper/iron ASAP, build the respective units and wipe out your neighbour (if you have a choice, go for the aggressive, psycho neighbour first, since you will be warring them sooner or later anyway). You can forego expanding in this case, since you will get the cities from them, so you won't have to settle yourself.
My plan is to emphasise military techs, build at most 4 cities, maybe get attacked which will strengthen my units, then choose the right time to expand by conquest. Maybe get Conquistador ASAP.
The "right time" is early in my opinion. As for getting the Conquistador early, there has been some good advice on this already in this thread (I haven't used the Feudalism slingshot before, but I'm going to try it in this game, sounds nice with the UU we have).
Any advice gratefully received.....
Take my advice with a grain of salt, there are better players than me, but IMHO Monarch is not as hard as it seems. I'm only playing Civ4 for a few weeks now and if I can win Monarch, so can you

(NB I've never played any of the earlier Civ games). I've read a lot of the articles in the War Academy, most of which are really helpful -- highly recommended!
Oh, and obviously you should listen to godotnut and the other daredevils around here...
--Sigi