I had iPhone 3gs on 3.1.3 it was kinda slow and laggy, so I decided to go on 4.0.1 and jailbreak using jailbreakme and i did it was SUPER slow cydia laggy and my iphone was crappy, so i rejailbroke and first thing i did was disable ios 4 multitasking and download backgrounder, and it has changed my iphone completely it was super fast and now cydia loads very fast, and my battery is much better
Ok so tips:
-Don't install stuff that slow down your iPhone or stuff that you don't know cause they will just mess up your iPhone
-Ok and other thing I tested is that when you turn off 3G or location services and push notifications respring/reboot your iPhone for it to work properly, I know that it works im not saying it doesnt even if you don't reboot/respring, im just saying that if you respring it'll make iphone start faster and work faster (and make your battery better)
-Another thing is for people who hate plain black background and want Winterboard if you are on ios 4 DONT download old winterboard themes, they will pretty much lag and crash your iPhone
-Always stay up-to-date with apps: cause if you have experienced bugs on lets say backgrounder the next update my have fixed those bugs and make it work better.
-TIP: Every 5-8 months restore your iPhone/iPod (but make sure there is jailbreak for when you restore) because I didn't restore my iPod in around 2 years and the battery started going from 100% to 0% in 20 minutes but when I restored it got to around an hour
-Too much used GB = Disasters: My brother got his ipod touch 16GB and filled around 13GB apps from cydia and app store and it was VERY slow and laggy compared to my ipod that i just newly jailbroke and restored mine was much faster so remember to delete unused apps but especially the ones from Cydia cause these are the ones that slow down your iPod/ iPhone.
-Airplane mode saves battery, A lot: So your probably wondering if im saying this stuff from my mind, well no it took me days even weeks to do testings, and from what I've seen Airplane mode made my battery last much longer of course more than normal because it seems as if the singal is taking up around 15% of the battery loss. But what I did was put airplane mode and turn off 3G, Location services, Push etc. And it made my iPhone much faster than usual and my battery lasted longer than usual so try it if you don't have anyone calling you at that time xD
-Brightness - Turn it down when you don't need a lot of light. If you are at 1 Am why do you need a lot of brightness, turn it down a little
-Accessibility Zoom/White on black - well I dunno if you noticed but I had both of them on while I was sleeping and when I woke up, my battery was drained a bit more than usual but the next day when i tried zoom by itself, it didnt take out a lot just a little bit of battery.
-TIP: Well I can say that almost all of Cydia apps might drain your battery, but mostly extensions (Winterboard, SBSettings etc.) they drain a whole lot, and thats the only reason why I don't use Sbsettings it drains a lot, so remember if you don't use the extensions, then delete them, only wastes battery.
-Charging while sleeping = not a good idea...because if you charge the battery more than it needs then the life span of the battery will become less, so if it were to stay for 10 months more and you charge it everyday while you sleep it'll be around 8 months.
But a good counter is to charge your iPhone when the battery is 15% or less then charge it and do that at least once a month and it'll make the battery much better.
-What takes up battery most: From what I've seen Wi-fi, or anything that uses wi-fi (push notifications location services etc.) takes up most of the battery so when your not using it and you have wi-fi on arond 10% should be gone, normal happens to me at all times, but I turn it off now when im not using my iphone.
-Auto Lock, VERY USEFUL (Trust me) - Well after I forgot my iPhone not in sleep mode (cuz i had never for auto sleep) I came back and found my iPhone at 10% when it was at 70% so from then I started putting auto lock for 5 minutes, even if I hate it, but really I was very scared that my iPhone backlight was going to need replacement cuz i left it there for about an hour, but luckily it was Okay.
-Backgrounding/Multitasking - These are a huge problem, when you have over 5 apps running at the same time, like lets say you want to background Skype, well thats okay, but skype and whole other bunch of apps that are made by Gameloft (big ones) it will make your iphone's battery die right away, iphone will be laggy and slow, and it may even crash to save mode. So don't back up a lot of stuff just when you need to check your mail for 2 seconds then its alright but for 2 hours, it will be very bad for your phone.
Playing games waste your battery - that's normal almost everyone here play games on their iphone or ipad once in a while or maybe all times, and ya the battery dies very fast, especially in large games such as avatar or splinter cell conviction etc.
Bluetooth - Yes bluetooth the magic happens here, since Apple didn't allow iPhones to use bluetooth transfer there are a couple of things iPhone can do which is connect to the headsets with bluetooth, for me it has been a horror using them, my battery dies fast I dunno why thats why I rarely use them anymore, and I rarely turn on bluetooth anymore on iPhone cause its useless, it only drains battery.
Jailbreak for ios 4.x:
Guide: On your iphone go to safari, type in jailbreakme.com, slide to jailbreak and your done!
For iPhone 3G (Any baseband)
Ipod touch 2G
Guide: install it from http://rapidshare.com/files/40062528..._0.9.5b5-2.zip <-- data-blogger-escaped-br="" data-blogger-escaped-windows="">
http://rapidshare.com/files/40062146..._0.9.5b5-2.zip <---- data-blogger-escaped-br="" data-blogger-escaped-mac="">
I think it is for Developers only, so I do not use and plus I think you should go with Jailbreakme because it is much easier and for everyone.
Cydia may not load sometimes/Crash
What I suggest you download on ios 4/4.0.1 (Apps that work)
Backgrounder - If you hate apple's ios4 multitasking
Sbsettings - Very good, but drains battery D=
Wi-Fi Sync (Paid) - Sync over Wi-fi excellent now compatible with Windows and Mac
Screen Dimmer (Paid) - Helps your battery last longer by dimming your screen
iFile (Paid) - Excellent if you hate SSHing access your root from your iPhone
Bosspaper - Does not respring itself need manual respring
Categories - If you hate Apple's folders, it is compatible with ios 4
Cydelete - delete Cydia apps from SB
Fontswap - Change Font (Note: does not change system font, must be a bug...)
iBlacklist (Paid) - Blacklist for iPhone!
InfiniDock (Paid) - add as many apps in the dock
InfiniFolder (Paid) - Go past the 12 app limit folders for ios 4
iWhiteboard - Draw over your iDevice
MyWi 4.0 (Paid) - Tether for iphone
PDF Loader Warning - Very important for your iDevice so that it doesnt get hacked from PDF's
Rename II - Rename apps
SnapTap (Paid) - Take photos/Videos using volume buttons
Winterboard - Good, but drains battery if you have themes on, and not all themes compatible.
UPDATE: Apparently Poof works on ios 4.0.1 for me try it and tell me if it works for you.
Note that I dont suggest you get all these, but I suggest you get some of those they are very useful if you are on ios 4.
Please comment and thank me if I helped
If you got more ideas, I'd be more than happy to add them just tell me and I'll try to add them.