I am considering getting a new beagle bitch pup, to go with Lou, my older bitch. Is there anything I need to take into account when introducing them. Lou is not overly dominent but i am a little anxoius, any advice would be greatly appreciated

i introduced my second dog to the first in our garden but then he's so gentle with every dog and person i just new there wouldn't be a problem. As for my last dog i new that that wouldn't be so easy as my second dog was quite nervous(are you managing to follow this lol).
In this situation i introduced them on neutral ground and had to take things very slowly, infact we had stair gates round the house until i was confident they would get on.
only you know your dog and how she is with other dogs but my advice would be to not let the pup try and jump on your dog, let them smell each other and see how they react. your soon know whether you need to go more slowly or not.
it is important though that you dog has time away from the puppy and vise versa, by putting a stair gate up you can seperate them if needed but they can still see each other.
A lot of dogs don't like puppies as they jump around and can bite, even though it's in a playful way so just keep an eye on things and stop your pup from doing this if needed. also your pup will learn good doggy manners and know not to push your dog too far but i expect you dog will put the pup in it's place if it gets silly and the pup will learn who's in charge.
make sure you give both dogs seperate time so no one gets jealous and this will help with the pups training as if your not careful the pup will look at your dog rather than you for how it behaves.
i'm sure you want have a problem but just make sure your always in the room with them to start with so you can control the pup.
i would suggest you get a male pup as there is less likely to be any problems further down the line but saying that two bitches can get along just fine as well if there's a big enough age gap but that is your choice.        

I always take my dog with me to pick up the new pup, that way they get the smell of the pup all the way home in the car. Everything else I agree with, vigilance is the key. I have to say that I have never had any problems with keeping bitches together however I am aware that that is not always the case.

I don't know about Beagles but I had a terrible time with 3 bitches - all of different breeds.  The 2 younger ones fought so badly I had to re-home one.  I don't know how old your existing bitch is but ohters on here have advised a gap of at least 3 years with same sex dogs.  If not I'd suggest getting a boy.

Thanks for all the help and advice, much appreciated!