We estimate as a team and then take the average
Good grief, don't take the average! That's not how planning poker is played.
Here's how I teach my teams:
- start with a brief discussion of the work involved
- play round 1: everyone shows their card.
- then the highest vote and the lowest vote each explain their rationale. Perhaps further discussion ensues.
- then play round 2: everyone shows their card
- repeat until there is consensus
- consensus does not necessarily mean everyone shows the identical card (altho we always enjoy it when that happens). If all votes are close but not identical, we sometimes define a rubric like "let's be conservative, take the higher number" or "let's go with what the domain expert said". (But don't "defer to expert by default" on the first round, at least not until the team gets good and comfortable with the whole process.)
Junior devs may feel uncomfortable when they are first asked to participate, and may need some coaching and encouragement that it is okay their estimates are different, and that it is helpful if they ask what might seem to them like "dumb questions", because their question will prompt an explanation that might bring up something that no one else had been thinking about when they made their estimates. When played this way, there is less pressure on junior devs because if they "get it wrong", that will be clarified during the discussion and this is an opportunity for them to learn by doing.
I don't feel strongly about whether to play in story points or in ideal days, but I do feel strongly that a Fibonacci deck should be used. Not only because the increasing bin sizes reflect how uncertainty grows as a function of size; but also because it's a lot easier to choose between 5 and 8, say, than between 5 and 6. The bigger gaps make the choices starker and therefore easier.*
*At least, it's easier once everyone gets used to the idea that it's not "accurate". It's not supposed to be accurate; it's an estimate. When you are estimating how much money you'll spend at the grocery store, you don't use accurate prices, "bread costs 2.23 and kleenex costs 3.86 and a candy bar costs 1.25". You say "ok, bread is about 2, kleenex about 4, candy bar about a buck, I want 2 candy bars so that's about 8, better bring $10 to be sure."
I introduced planning poker to my teams in order to help them be more comfortable with estimation, and learn from each other how to do it well. But honestly, the benefit in knowledge sharing and scope clarification is so high that at this point I almost consider the estimation to be a secondary goal.
I hope this helps! Good luck, and try to have fun when you play.