I'd seen many article about setting up the guitar for dropped tuning.Is it necessary to do so if i want to tune my guitar from standard E to lower tuning?And if that's the case what do i need to do to setup my guitar to lower tuning?*i'm not an expert so i would appreciate it if someone can explain about this setup thingy*
When they refer to "setting it up," it usually means removing the backplate of the guitar and changing the tension of the springs. I'd make sure you know what you're doing first before you start adjusting though.

However, if it's only slightly lower than normal (like D standard for example,) I don't think it's necessary to adjust anything.
depends slightly on your guitar but typically:

strings first
if you're going more than a step down in tuning, you will want to use thicker strings to increase the tension so the neck doesn't bend further back, this will help regulate the action and thinner strings can start to sound fuzzy the lower you tune down

thicker strings might not sit in the gaps in the nut, if thats the case you might need to file them slightly larger, you can get tools for this, i have done it with a stanley knife once.
if you leave jagged / sharp edges in the nut that can ruin the strings though so do it right :p

truss rod next
tuning down reduces the tension on the neck and you may need to alter the truss rod as well as increasing string gauge to maintain the angle of the neck, do this carefully by slight adjustments to not damage the neck, several types of truss rod so google how to for your guitar

intonation can be changed by these adjustments so you will want to use a tuner and adjust the position of the saddles on the bridge to get it right, again google this
It all depends on whether you plan on making this a permanent change, or if you're thinking of messing around with different tunings for a little while and then re-tune it up to standard E again

If you decide to stick to a lower tuning the one thing you WILL have to do after is re-set the intonation. The next couple of steps depends on whether you want to change to another string gauge: most professional musicians who play in lower tunings have their guitars equipped with .011s, .012s, .013s or even higher, because standard string gauges get all rubber band-ish when you detune 'em which affects the tone and playability of your guitar. Don't worry about not being able to bend your strings anymore and all that stuff -> that's just the case when you use thicker strings and tune 'em up to E

If you do switch string gauges there's a bunch of things you might have to do, like checking out the intonation again, widening the slots at the nut with a tiny file if they're too small for your new strings (not always the case), adjusting the spring claw (only on guitars with floating bridges) and, if you're experiencing problems with fret buzz, perhaps adjusting the string height or maybe even the truss rod (not recommended if you're a total noob at setting up guitars, and if you decide to do it make sure to check out the forum again)

That's about all the adjustments I can think of...

Edit: looks like funeralllllllll beat me to a couple of things. The only thing I'd like to add to his contribution is that truss rod adjustments aren't always necessary -> for instance if you only tune your guitar ½ a step or even an entire step chances are your neck won't shift at all (especially if you compensate by using heavier strings), thus making a truss rod adjustment unnecessary. Some guitars just have really sturdy necks...

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Last edited by shwilly at Jul 8, 2011,
Well i am going to make dropped b as my permanent tuning so i guess i 'll just have to re-set the guitar current setup?am i correct?oh and by the way thanks for the tips guys.all of you.