Your pianist pal wants to try out some repertoire and has been eyeing your Bechstein hopefully. Sure, come over and play it through, you say. We'll invite some friends and have a few drinks and it'll be lovely...
Check how many you can seat. Be realistic. A piano can be loud in a smallish room; you don't want people actually sitting underneath it. See how many chairs fit in at a safe distance, and consider the ratio of sofa width to guests' average behinds. Don't forget to ask your performer if s/he wants to bring anyone. Chances are, if it's midweek, you'll end up with an audience of mingled neighbours and arty types or similar - which works well, provided (achtung!) that they are on speaking terms with one another.
People need to eat, so plan your menu and take everyone's dietary requirements into account (veggie, GF, etc...). Recommended: easy protein - cold meats/cheeses/smoked fish - plus non-dairy dips, bread/crackers/rice cakes, prepared salad, crisps, nuts & raisins. You will need soft drinks, plus wine of at least two colours. Balance your green credentials and decide whether to use disposable paper plates, or crockery that needs washing, but isn't wasteful of trees. And make sure there's something to feed your pianist upon arrival; the sooner you offer him/her that cup of tea, the better.
Check whether your piano needs tuning. (The answer in 99% of cases will be 'yes'.) Make sure you book the tuner at least three weeks in advance, preferably longer, because these guys seem to be really busy these days. If it proves impossible to get your piano tuned, but it sounds OK-ish, then you may get away with it, but do dust it so that it at least looks decent. Clean behind and under it, too, especially if you don't very often and you have a cat...you never quite know what's going to turn up...
On the day, do your shopping early so that the supermarket hasn't run out of the necessaries. Fix what time your pianist wants to arrive, because s/he will need at least an hour to get used to your piano and then might want to rest/refuel before the audience arrives. Set up the room earlyish, too; you don't want to be clonking about, carting chairs, when pianist is practising the trickiest bit.
In an average-sized living room, it is probably best if you don't put the piano lid fully up, unless everybody has brought ear protectors. Many modern grand pianos have a selection of stick lengths for the lid; a fine pianist playing colourful repertoire will be best served by a fuller sound than if the lid is kept resolutely down, but it can be most sensible to choose the shortest.
Arrange your buffet on the table before people arrive so that you're not unwrapping smelly cheeses while you welcome them, but don't forget to cat-proof everything with copious quantities of cling-film. If your spouse has scarpered at the idea of this event, or is busy elsewhere, so you're organising the whole thing alone, encourage people to help themselves to drinks, especially if they all pitch up at once.
Try not to start much later than the time your performer has requested, because he/she may get nervous if things are protracted, and the whole point is to put him/her at ease. Remember to give pianist a five-or-ten-minute warning before you're ready to start. Once everyone is settling with a drink, encourage them into the piano room.
You might wish to confine pets to another room while the concert takes place. Sensible animals keep their distance from live music, but some importunate ones march in and demand very vocally that all this noise must cease forthwith, and with immediate effect. No prizes for guessing who I'm thinking of.
Interval, or not? Be guided by your musician: if s/he wants a short break in the middle, agree. You don't know what his/her innards do. One pianist I know used to compare concert-giving to colonic irrigation.
If someone is late, you can do one of several things. You could leave the door on the latch and encourage latecomers (by text) to sneak in during an appropriate break. If you don't want to do that, then tell them to text you when they arrive, keep your phone open but SILENT and make sure you take a chair near the door so you can slide out and let them in.
After your pianist has finished, make a fuss of him/her. A house concert may be in a house, but it is still a concert and any musician worth his/her salt will feel obliged to deliver the full goods, whether it's for 800, 80 or 8 people. Frankly, the least you can do is give him/her an Easter bunny.
Next, zip out to the kitchen and take the cling film off the buffet dishes, keeping the cat clear. Furnish people with drinks and plates and encourage them to tuck in. If there's anything left over when everyone goes home, offer your pianist a doggy bag. If everyone is having a good time, it's a great feeling because you and your musician have given them a lovely evening to remember. But make sure they don't miss the last train.
Finally, wash up. By now it's gone midnight and you're probably wishing you'd used the paper plates after all.
The next day, try to have a lie-in. Then thank your musician (though best not to ring too early). It may be hard work hosting a house-concert, but it's not half as hard as doing the playing.
Last, but by no means least: huge thanks to our own pianist pal Anthony Hewitt and our old friend Alexander Ivanovich Scriabin for a stunning evening of magical preludes yesterday!