Dr Isis speaks the truth. Collaborators are a tricky thing, especially for newer/untenured scientists.
You do need to be careful. You do need to make sure that the BSD's or other malevolent life forms do not suck you dry and leave you covered with spots. When a senior person, where you are, asks to you "to collaborate", first get the details. What are you being asked to do? Do not take their word that its just a "bagatelle" and "you can do this in your sleep". Think carefully and ask yourself: how much time? what if it doesn't work? who's paying for supplies, who's doing the stats, etc. Likely you have some marvelous skill (that's why they hired you). I was first trained in maths and stats, and was always getting asked to "just do this little bit". It took a while to sort through and figure out what I could do easily (ie 1-2 hours for a middle authorship) vs. things that were an on going quagmire.
Be equally leery of the "could your tech just run this sample?" request. Remember you are paying for that tech/asst/whatever out of your precious seed money, or starter grant. You need to be investing in yourself and your future. Do not be fooled that "helping" is going to make a difference at tenure time. If your tech has some spare time, maybe ok. But then, what's your tech doing with spare time anyway? Figure out something to keep 'em busy. Sometimes throwing a sample in a New Shiny Glittering piece of equipment is easy. The results come printed out nicely. Its very sexy and everyone is happy. That's great.
Also, ask about the outcome/product/final stuff. Who writes the paper? What's authorship going to look like. Remember, there is lots of time to do favors once you are tenured. This is very hard. It makes you sound ungrateful for the attention of the BSD. It makes you sound greedy, and grubbing and all sorts of nasty things. But! in the end it is your CV that is evaluated for tenure.
If you decide to say no, it can be tricky. You need to be honest, but not insulting to BSD. Things that you can say:
I'm sorry but I am just getting my lab going, and I am not sure about running that right now
I'm sorry, but I am so focused on analyzing my prelim data for my grant that I can't really do anything else.
I am writing my grant and its a struggle, would you look at my Specific Aims?
My dog eat the software, and the replacement is on backorder.
If you make the turn-down about you and not about their science, it will usually go OK. If it doesn't, go to your ally in the department (you do have one, don't you?) and lay it out. Do not say "you are a greedy micro-dick and I am not going to let your idiocy sink my career". Bad move.
The biggest problem you will have is saying no. Start practicing now.