To do that, the best is to cut your object in several smaller parts that won't need supports at all whenever it's possible.
This is of course mandatory if your printer size isn't big enough for your project, but is something I will also recommend to those who have bigger printers.
The reason, in addition to save on print time, is to not loose hours (or even days) of print if ever something goes wrong during the printing process.
And everybody with some printing experience knows that unfortunately printing failures are numerous and can happen...
By printing your object in several parts you will only loose a portion of your project in case of a failure.

I have several objects that I'd like to print big.
Among them I have this sculpture from the artist Herman Makkink, that everyone with a minimum of cinema culture will recognize, from the great and awarded "A clockwork orange" movie by Stanley Kubrick.

Rocking machine

I 3D reproduced this sculpture in SketchUp a long time ago based on photos, and allready printed it at a small scale (10cm).

But now I'd like to print it 40cm. This is half the size of the original sculpture seen in the movie.

The sculpture will have to be hollow to be able to introduce some balancing mechanism inside it.
For my 40cm version, the walls will be 5mm thick.
You can use Meshmixer for the hollowing process. You could also use 3Dbuilder but the inside surfaces are coarse and this won't be good if I want a ball to be able to smoothly roll in the inside.
Next you have to plan your different parts in such a way that they will need the bare minimum of supports to save on time and material.
I decided to cut it in 9 parts like this :

9 parts print

In my case, only 3 parts will need supports :

P1 print
P8 and P9 prints

Finally, and to help in aligning back all the parts before you glue them, it's a good habit to include some keying in your design.
At first I was thinking of something like this that took me nearly a all day to design in SketchUp :

Keying

I then realised that I could simply add holes in the walls in which I will use small pieces of raw 3mm filament.
It made the keying design process way much simpler !

Simple keying

Time to print...
You want to avoid supports as much as you can.
Even parts like this one don't need supports :

No supports

And on parts that are impossible to print without supports, reduce them to the minimum.
I usually make support structures only for angles above 80°.
Your printer should be able to print correctly even at this extreme angle :

Extreme angle

Here are all my printed parts :

Printed parts

And here is the assembled sculpture before gluing anything just to check :

Temporary assembly

The next steps will be :

  • gluing parts (minus parts 1, 6 and 7)
  • introducing a balancing mechanism inside it
  • do some balancing tests
  • gluing the remaining parts (1, 6 and 7)
  • sanding
  • painting
  • epoxy resin covering

I will soon show you another case of a big print and how I minimised the print time by cutting my object into well choosen parts.
Until then, have fun printing big things !