Art fans Do It at Manchester International Festival

An instruction from US artist Adrian Piper is placed at the gallery entrance

Draw all the curtains on the planet. Smile at a stranger. Reinvent life. Start a rumour. Do nothing.

These are among the instructions written by 250 artists for the public to carry out as part of a 20-year art project called Do It.

In Manchester Art Gallery, I have squeezed a lemon on the upturned point of a bicycle seat, got on my hands and knees to make a ball from soggy newspaper and clutched a meteorite while contemplating the universe.

You may think these sound pointless. You may think they sound fun. They are neither. They are art.

Well, OK, they are mostly pointless. And some are quite good fun. And the artistic merits of my actions are rather dubious.

But I was only carrying out orders from artists as part of Do It - a kind of DIY art movement based on instructions from artists like Ai Weiwei, who tells us how to spray-paint over CCTV cameras, and Tracey Emin, who suggests making a sculpture out of bottles and cotton.

The project is now the basis of an exhibition in Manchester, where visitors are invited to Do It themselves in the gallery, or take home sheets of paper or a thick manual instructing them how to Do It at home.

Visitors are invited to squeeze lemons on the point of a bicycle seat

The lemon squeezing is done at the behest of the German artist Andrews Slominski. The bicycle seat is mounted on a gallery plinth, which soon gets covered in juice and pips.

In another corner, a message from Yoko Ono implores us to write a wish on a small tag and tie it to an artificial Wish Tree. Wishes that have been attached include "I wish for love", "I wish to find what I'm looking for" and "I wish to get through today and not be assailed by instructions".

I am torn between two wishes, so I write down both, one on either side of the tag. "I wish for a peaceful future" on one side, and "I wish for cake" on the other. (It was lunchtime.)

Elsewhere, I wait patiently to follow an instruction to climb a ladder to peer into a mysterious giant white cube. When I get to the top, the cube is empty except for a sheet saying: "Wherever you went there was a strong smell of petrol."

Not the meaning of life after all. Thanks, Ilya Kabakov.

In another room, a meteorite is stuck to a magnet on the wall along with a message from the Scandinavian artist Olafur Eliasson, who is best known for creating a giant sunset in the Tate Modern Turbine Hall in 2003.

It is a heavy, metallic, warped chunk. As Eliasson points out, it is the first time I have touched something from somewhere other than this planet.

"Your imagination of the meteorite's trajectory - from outer space into this world and into your hand - makes it touching to hold in your hand," the message reads.

"The longer you hold it, the more incredible it becomes. Pause."

It is incredible!

Yoko Ono asks visitors to tie their wishes to a tree

"While holding the meteorite, try to see yourself from the perspective of the orbiting asteroid belt. Think of this as your multi-verse point of view. Pause."

I am a speck of dust. I am insignificant.

"Take your asteroid perspective. Be outside and inside yourself at the same time, present in the multiverse.

"Become an asteroid. Do it."

I am an asteroid. I am hurtling around the universe with all those specks of dust on Earth below me.

It is a cosmic and moving experience.

I hand the meteorite to the next person, crash back down to earth and go for lunch.

I leaf through the 450-page manual, which has collated all the instructions that have been written by artists since 1993.

Some are very practical, like Ai Weiwei's spray can-on-a-stick contraption, or recipes, like the sea bass curry I have for lunch, which is made to a recipe by the Indian artist Subodh Gupta. Very tasty, but a work of art?

Some instructions are deliberately impossible or outrageous, like Waltercio Caldas' "draw all the curtains on the planet at the same time", or performance artist Marina Abramovic's recipe: "Mix fresh milk from the breast with fresh milk of the sperm. Drink on earthquake nights."

Luckily Manchester is not in an earthquake zone.

I like Gilbert & George's Ten Commandments, but fear they are on the ambitious side: "I: Thou shalt fight conformism. II: Thou shalt be the messenger of freedoms. III: Thou shalt make use of sex. IV: Thou shalt reinvent life." Etc.

The Manchester gallery has a room in which to play games created by artists

Others are impractical or incredibly involved.

Maria Jose Arjona wants me to live in a space that is "susceptible to the sacred" for several days and nights, eating only fruit and drinking only water.

Roger Hiorns suggests grinding a steel engine part from a passenger aircraft into dust. Ayse Erkmen invites me to buy or rent a red Ferrari and crash it into the back of a grey Fiat Palio.

Perhaps I can get an Arts Council grant to carry out these instructions.

The question that arises, which may have already crossed your mind, is - what is the point? Why should we Do It?

Ilya Kabakov asks people to peer into a mysterious white cube

I speak to Hans-Ulrich Obrist, the Swiss uber-curator whose idea Do It was. He talks about "art for all" and democratising art by taking it out of the gallery and into the hands of ordinary people.

Yes, but if I squeeze a lemon on the upturned point of a bicycle seat, is that supposed to make me think differently about the world, or question the instructions I normally follow? Or what?

"It's got to do with unexpected encounters also," he begins before launching into an artspeak ramble.

He concludes with the words: "So it goes somewhere from Duchamp to Fluxus to the algorithms of the digital age." I sense his giant brain fizzing with energy, but I am none the wiser.

As well as offering the occasional moment of enlightenment, like the encounter with the meteorite, one thing I can say for Do It is that perhaps, by presenting us with these bizarre, unrealistic instructions, it makes us question the sense behind the orders we normally follow in our daily, rule-led lives.

Plus, especially with a room in the Manchester gallery filled with artists' weird and wonderful games, Do It is good fun. But if good fun equalled good art, then galleries would just be full of fairground rides.

In search of further enlightenment, I decide to take the Do It manual and carry out the instructions by Douglas Gordon (how to make tequila slammers) and Mircea Cantor ("Burn this book ASAP").

Do It is part of the Manchester International Festival and it is at Manchester Art Gallery until 22 September. Do It is also featured on digital arts channel The Space, which will host a live stream from the exhibition from 10:30-18:00 BST (09:30-17:00 GMT) on Friday.