I'm sure there are several methods, but what I do is I just grab some low weights, "warm up sets". 50 - 70 % of what you intend on lifting. When starting out as low as 4-5kg, the warm-up weights would therefore be as low as 1kg or 2kg per arm. Just do a few of those just to get some blood flowing through there

That's it, really. Works for me.
Pushups are also a good choice, but I don't like to do them because I always get some discomfort in my left elbow