It all depends on what you want to do and what tuning. You can just drop the E string down to D, so it's drop D with the lower string. and you could drop your B string to A to double drop.

Or if you are using a tuning lower than B just use the Low string as your main. Experiment with what works best for you.

Have fun!
I don't think you'll need to change your tuning much unless you feel like trying some Drop A on the 5th string.
Professional lurker since 2009.
AEADG - Drop A - or standard with a drop A
ADGCF - Standard D tuning
GCFBbEb- Standard C tuning
GCGCF- Drop C with the low G on a five string.
GDGCF- Im sure this is used. Don't know if its drop G or not.

And seriously don't think you need to go any lower than this. And if you want to go any higher that standard BEADG I would get a six string.
Put your lowest string as what the guitars play, and keep the rest in standard- it will help you immensely in terms of coming up with your own licks and such. It did with me anyway, I play with drop C guitars and I tune my bass to CEADGC; it forces you to think outside the box and not just play the same as the guitars. And it's much more fun.

That's for tech metal though, if your band plays simpler stuff I'd just keep it in B standard. At any rate I'd just avoid playing in the same tuning as the guitars (unless they tune standard as well), as it forces you to use your brain more when writing and playing your bass parts.

Plus it looks swish as hell when the bass is playing something different than the guitars on stage
Drop A and DADAG come to mind.
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if we're talking open, I like ADADC# or BF#BF#D
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EADGC is fairly popular
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EADGC is fairly popular

I'm surprised it took this long for someone to say this.

I actually have my 5 banger tuned EADGC. You can NOT do this tuning with standard strings, you must use a set specifically for high C tuning.
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