I saw a similar topic elsewhere and wondered what this community would say:
You are playing a bass for the first time. Could be new, could be someone else’s, or maybe you picked it up at a music store.
What riff, bass line, scale, or technique do you use to connect to the soul of that bass?
Personally, I like a little “Wicked” Wilson Pickett.
I always do the same thing when I pick up a new bass.
Play each string open one at a time
Play a scale or two inb varying positions
Then just a random medley of basslines I know, or improvising something out of the scales.
If it’s at a big box store then it’s just noodling around, maybe a couple of phrases of the chicken. That said when I already decide to buy then I actually would sit down and play a few of my “put it through the pace” songs. These are the songs that has good playing up and down the neck and I play them enough to know the difference between each bass. I can notice the little differences is it too fast, to slow.
When I bought my Cutlass at the Shop, @T_dub was there with me, cash in hand, I asked the shop if I can connect my track and play along. This is important because I can feel how it sits naturally in the mix. In my case, the Cutlass was just a phenomenal bass and the decision was made very quickly.
I did the same thing with buying the amp, at the same shop, I actually brought my bass to test the amp.
7 Nation Army! 
I get shop-freeze and forget anything I can play so just noodle around. I try to explore the neck and see how it feels. I’ve only bought 2 bass and didn’t know how to play for my first. With my second, the shop was getting ready to move so only had a crappy little amp. I loved the feel of it and still managed to enjoy the sound. I think I played it for maybe 30 mins and just loved it more each minute so it came home with me.
The Deee Lite Groove is in the Heart groove. It makes look like I can actually play 
A colleague has just bought a £2,000 Rickenbacker. He brought it to the office and I tried to play Groove on it, and couldn’t. The bass felt horrible. I had another go on it last week - he had had it properly set up - but it still felt cumbersome under the fingers and I still didn’t like it. The upshot is that a) I would be unlikely to buy a Rickenbacker and b) Groove proved itself to be a pretty good test riff! This colleague also has a G&L L-2000, now that’s lovely and Groove grooves on that bass!
Oh, I do want to learn the Star Wars Imperial March melody at some point. I think that would be fun in a shop 
Gandalf (
) once said: You do not find the Bass: The Bass finds you. 
It’s like love from the first view: You don’t need a specific Bass Line or a ritual for playing the One Bass; the Bass itself is the gift enjoying it to be played. If you like it, go for it. 
Wish you all the Bass 
DLiqacy
I start with what I think is some scale or summat that’s stuck in my head. It’s… well, picture this as tab: E:1,4; A:1,2,3; D:1,3;G:1,3. Then I play that up and down the fretboard in various positions. Then the major scale in various positions. Then I just riff for a bit, throwing in various snippets from songs I’m working on. If I’m feeling bold, I’ll toss in some root/octave slap/pops.
The latter stuff changes, but that thing I think is a scale and the major scale never changes.