Here are some suggestions on how to play Assassin's Creed quickly, so you can spend less time on the repetitive stuff and focus on whatever you're trying to accomplish (Conversationalist, assassinations, etc.) I don't claim to be an expert on speed play. If you have other ideas, please send them to me and I'll try to include them.
MASYAF
There has been a good deal of research into how to get from Al Mualim's desk to the Kingdom in the least amount of time. After early steps by myself and Ian, he came up with this gem (1:34 to end):
(Good luck hitting that chimney at 2:36!)
You'll have to do this at least nine times over the course of the game. In Memory Blocks 2, 3 and 4 there's an extra delay. An Instructor meets you at the exit from the Library and transports you to the Fighting Circle (just below the railing). The Xbox 360 keystrokes to quickly exit the tutorial are: Left Trigger, Start, B, D-pad up, A. For PlayStation 3 users it's: L1, Start, Circle, D-pad up, X.
KINGDOM
In Memory Blocks 2 and 3 you have to manually cross the Kingdom three times. The fastest way is to use a horse (duh) and gallop at full speed. When Exposed, just ride on. If you see guards up ahead forming a road block, they usually leave a gap to their left and/or right. Slow down to figure it out and then ride around them.
The routes from Masyaf to Damascus and Acre are pretty obvious: stay to your left or right, respectively. The ride to Jerusalem is longer and has some turns that are easy to miss. Refer to this map for the shortest routes:
Starting in Memory Block 4 you can hyperspace across the Kingdom by selecting your destination in the Animus. Take advantage of this feature.
There's a mandatory Viewpoint to climb in Memory Block 2 as soon as you leave Masyaf. Other than that, you shouldn't have to climb any Viewpoints in the Kingdom.
ENTERING/EXITING CITIES
I've said before that there are four ways to get past a guard post:
There are actually two other ways that can be even faster:
If you enter the city Exposed you will lose some time Hiding, but it's a good option to consider if you'll be Sprinting clear across town anyway.
The dismount cheat (courtesy mrtawnik on GameFAQs) really works and allows you to enter Anonymously. The trick is to get that high dismount where Altaïr puts his feet on the horse's neck and jumps straight over its head, usually rolling when he hits the ground. You want to hold Right Trigger (or R1) and keep the Left Stick straight up. Do not Gallop. Continue holding Right Trigger and Left Stick as you hit B (or Circle) to dismount. It also seems to help if you have a high camera angle. :?: Practice the dismount in the Kingdom until you get the hang of it.
The first five methods of entering a city are illustrated in this video by iXzion. I demonstrate the dismount cheat at the beginning of the following video:
Al Mualim and the Animus tell you to check in with the local Bureau Leader upon arrival. This isn't necessary. Proceed directly to the District where you will do your Investigations.
You do have to visit the Bureau both before and after an assassination. Afterwards, the Animus may ask "Fast forward memory to Masyaf?" Always answer yes. There's a rumor that you can say no and ride directly to your next assassination. Trust me, it doesn't work that way.
GETTING AROUND TOWN
Ubisoft struck a good balance between streets and rooftops: both are equally frustrating to navigate when you're in a hurry. I use a combination: hop rooftops until you encounter a large "hole", and run streets until they curve away from your destination.
At street level, take advantage of pedestrian "highways" which are the wider streets that stretch across the city. Anywhere you can walk you can also run without attracting attention. If you're not Blending you should be Running! Just be careful not to bump into guards. Sprinting is sometimes an option. Civilians that are facing you will jump out of the way as you approach slightly off center. An Informed guard will go into Open Combat if he sees you Sprinting, so keep an eye on your Witness Indicator to know when it's safe to Sprint.
When you stop Running or Sprinting, Altaïr gradually slows back to a walk. As he decelerates, you can safely Gentle Push through jar carriers. The same goes for Blending with Scholars. You can Sprint right up to them and Blend at the last instant. (tips courtesy IanXO4)
As far as rooftops, the key is to keep moving horizontally rather than up and down. Try to jump between buildings that are approximately the same height. When an archer gives you a verbal warning ("You have no business...") you have 10 seconds to get outside his 15 meter radius of vision. That's an eternity. Unless you plan on sticking around this area, don't bother killing the archer. It will just slow you down.
SIDE MISSIONS
If you can live with a blurry map, don't climb any Viewpoints. Otherwise, climb every other one to bring your map into focus. It shouldn't be necessary to Save any Citizens except the mandatory one in Memory Block 2 outside of Damascus.
You have to do two Investigations per District in Memory Blocks 2-3 and three Investigations after that. Below are the Investigation types sorted from fastest to slowest:
Use an online guide (because your in-game map will be incomplete unless you climb all the Viewpoints) and plan a tour of easy Investigations that ends near the Assassin's Bureau. I'll make some specific suggestions below.
For Interrogations, you don't need to follow them to a quiet location. You can often start the fight immediately. Use grab and throw to control the location of the fight to minimize interference from thugs and guards. Each grab and throw counts as two punches. (contributed by IanXO4)
After a successful Save Citizen and before/after Informer missions, you have to talk to the person you're helping. Run and Jump at him/her and pull the Left Trigger while in mid-air. They will start to talk but will be interrupted when you bump into them. You can also interrupt them by hanging and dropping on top of them. Then you're free to go. (tips courtesy of cheezzhead and IanXO4.) See this video demonstration by brunovesgogta:
BATTLE OF MASYAF
The early parts of the game are "on rails". You have to complete the Animus tutorial, etc. The first opportunity for a major shortcut is the Battle of Masyaf. When Rauf tells you to "Distract the Templars", just ignore the Templars and race down to the main gate like in the video above. When you get to the bottom Abbas says, "Break off the attack and return to Masyaf!"
TARGETS 1 THROUGH 9
The general advice above pretty much covers it. All you need now are maps of the easy investigations. These are the ones I recommend:
TARGET 10 (SPOILERS)
At the beginning of Memory Block 7 a Masyaf villager says "Gone to see the Master." You can get a head start by walking up the hill during the cutscene. The villager will follow you for awhile and keep talking. It's hard to see where you're going because the camera focuses on him. This video demonstrates the technique:
On your way up the hill a big fight breaks out. Once you defeat those guys, a second group drops down from the ledge above. This second fight lasts 35 seconds regardless of who's winning. Just don't die for 35 seconds and you will be rescued.
When you finally face your last target one on one, the Hidden Blade counter is the only way to fly. It's a five second fight: loser attacks, Altaïr counters, loser dies. If he Grabs you first, just let him Throw you so you can try again on the Counter Attack. Counter Grabbing or using any other weapon means chasing him all over the garden while on the verge of desynchronizing.
KNOWING WHEN TO QUIT
A new Memory Block begins when you enter the Animus and see Al Mualim at the Library, not when Desmond wakes up. So if you want to finish a Memory Block before turning off your console, do so while in the Animus. Otherwise you'll have to replay the Abstergo scene the next time you load the game.