What I do personally (and this is not advice from me to you) is that I try to reinvest the divi in the same company from whence it came. However, there are a couple of caveats to that:
I check whether I still feel that company is a good place for my money
It may be that the divi isnโt enough to buy a new share (in companies where you canโt buy fractionals) so the question then becomes a bit more complicated. In this case, I look for the next best thing that is low enough in price to match the divi in my portfolio, then if that doesnโt work, I look at my watchlist.
You could keep the divi as cash until the next divi payment too, or until you top up your account to be able to buy a whole share.
I like dividend stocks for a couple of reasons, firstly instead of automatically investing the money back into the stock it came from it allows me to decide myself where to put it and secondly because it does motivate you somewhat if you see money coming in, even if other parts of your portfolio are going down.
I do similar to TheRaven except that I skip step 1. I simply add whatever money I have in dividends to the pool of money from which I make new purchases, then I check my watchlist for whatever seems like the best buy at the time and invest where I think it makes most sense.