When it comes to painting new plaster and the plasterer has been nice enough to have left you a nice flat smooth surface, then why not compliment the plaster with a top quality paint finish.
To do this we will need certain tools.

Tools
1 x 9” paint roller with a short pile longlife sleeve
1 x roller tray or scuttle
1 x roller pole
1 x 3”or 4” paint brush either the good quality synthetic or pure bristle Hamilton perfection
1x 2.5ltr paint kettle
1 x bucket or old clean 10ltr paint container

Protection
Dust sheets folded over double, masking tape for pre finished surfaces, sponge ,bucket of water and cloth to mop up any accidents
.
Materials and sundries
Good quality trade vinyl mat or silk, a quality filler (tetrion), abrasive paper 120 grade, decorators caulk.

When painting new plaster the 1st coat is equally as important as the top coat if not more.
Because if you don’t thin the paint down with water you will have a rough orange peel effect texture that will totally ruin any chance of a nice smooth finish.

Step1
After putting dust sheets down folded double for added protection and organizing your tools for use in middle of the room in one spot,
Empty paint in to a bucket and stir in approx 20% water (to thin the paint down to be able to absorb into the plaster) fill the paint tray to the level don’t overfill, and also Half fill the paint kettle for cutting in brush work.

Step2
now your ready to start the 1st coat (mist coat), cut in with the brush all around the room, around door frames above skirting, a straight line to the ceiling, around windows, taped up light switches and sockets being careful to feather out the edges of the paint as you go as not to get runs or ridges of paint, and make your cutting in strips about 6” wide. When all the cutting in is done then roll the walls making sure you overlap your cutting in. That is your mist coat complete. Because you thinned the paint down the paint absorbed into the plaster leaving a smooth texture.
Step3
Start at 1 point in the room and work from there going all the way round lightly rubbing the wall down of any grit so they feel smooth to the hand, then mix up some filler and fill any cracks, dents or holes. Then get a sealant gun and decorators caulk and fill, tops of skirting, sides of door frames and I put a thin caulk bead along the ceiling line to make it easier to get a tight straight cutting in line.

Step 4
Go around the room and rub down all patches of the filler to a smooth flush finish, dust off the skirting and any other horizontal surfaces, then touch in the filled patches with the thinned down emulsion.

Step5
2nd coat can now be applied in the same way as the first, you can use the paint neat or if you slightly thin down with water by about 5% it will give you a smoother finish as the paint is thinner. You will also find it faster and easier to cut in a straight line to the ceiling with the paint slightly thinned. I thin my 2nd coat down slightly and roll a section of wall about 6ft wide and exhaust the roller of paint then go back, and back roll(lightly rollover again while paint is whet and roller is exhausted) each section, which takes out the roller texture even more.

Step6
Same as step 5 you can use neat or thin the paint down, when I am trying for the best finish I slightly thin down again and also back roll again.
The thinning down ratio is based on using a good quality trade paint like dulux or crown and does not apply to retail paint or any cheap brand that is thin already