First off, welcome aboard.
Second, there is no magic number for what wattage is safe. If you try running 20 watts on an old ce4, you are going to have a REALLY bad time. If you try running 20w on something like a TFV4(for perspective, I am currently running my TFV4 with the quad coil at 110 watts and happier than a pig in a mud puddle) like I am using right now, you probably won't even get it hot enough to produce any vapor at all.
Since you said you are running a pico, I am going to assume you are using a Melo 3 tank. If that is the case, the 0.3 ohm coil has a factory rating of 30-80 watts. Realistically, I wouldn't recommend going all the way to the top end of that range, but you should be fine anywhere under 50 watts unless you are hardly moving any air over the coil. The main thing to look for is that you aren't getting burnt hits. If you do, you will know it. It will leave a horrible taste and your throat will be pretty unhappy with you. If you are getting smooth hits with nice vapor and flavor, you are doing great. The best way to find the upper limit of the wattage you can safely run for your coil is to start at a low wattage, and then raise it a little(just a few watts at a time) every few pulls. When you start getting even the slightest burnt taste, you have gone too far. Back it down 5 watts and try again. If you don't get that taste anymore, you have found the limit of that coil. If you are happy with the vape you are getting right now, I would just tell you to stay where you are unless you just want to play around some(personally, I am guilty of always wanting to play around).
In addition to all that, most flavors work best at different wattages. Some will really come alive at lower wattages, and then taste like crap at higher wattages. Some will taste like crap at lower wattages, and be amazing at higher wattages. Just start low, work up slow, and find the sweet spot for the juice and the coil. An example of this is my peppermint juice, strawberry juice, and grape juice in my TFV4 tanks. The peppermint is great at 70-80 watts, but becomes nasty at anything over 90. My strawberry is just a "meh" feeling at 70 watts, but when i crank it up to 90-120, it is an excellent flavor. Then I have my grape flavor that doesn't really seem to care what wattage I run. If i go 70w, it is pretty good and stays pretty much the same all the way up to about 130w. My cinnamon roll juice gets good around 50-60 watts, becomes excellent at 60-70 watts, and then starts being horrible after 75w.