How far apart should I plant my screen trees?
Generally allow 80cm-1mt between each tree,  this allows them to grow into each other and provide a total screen when fully grown. To get your screening tree's up to maximum size as quickly as possible, plant into well drained fertile soil, and water in well.  Although there is different maintenance and care instructions between species, as general guide you should aim to keep the soil barely moist.  Do this via mulching or drip irrigation.  Another great form of watering to consider is placing at 30-40cm length of 50mm Agi Pipe next to your tree at planting.  You can then water into the agi pipe to allow water to go straight to the root system and drain off the surface. 
How tall are screen tree's in each pot size?
As a guide only:  20cm pots stand 40-60cm tall,  25cm pots stand 70-90cm tall,  33cm pots stand 1.2-1.4mt tall, 40cm pots stand 1.6-2mt tall and 50cm pots 2mt+  Always check with you supplier if you need plants at a specific size. 
How do I look after and maintain my Screening Trees?
After planting, continue to water enough to keep the plants barely moist. This can be done via drip irrigation watering, or hand watering 2-3 times per week.  If hand watering, one of the best ways to ensure water gets directly to the root system is adding a short, open ended length of 50mm agi pipe next to the tree at planting.  This allows you to water into the pipe, safeguarding water running directly to the root system. Mulching is also a great way to keep your screening trees, cool and moist.  
Fertilise with organic plant food in Autumn and Spring,  at recommended rates.  And consider watering with Seasol every 6 weeks for additional nutrients. 
Finally, trim regularly.  The last thing you should do is wait until your screen tree has reach the desired size and begin pruning. This would leave your plant bare and woody.  Instead,  regular light trimming will help your plant stay dense and bushy, whilst encouraging further growth. 

What are the best plants for total privacy?

See Online Plants for their top ten screening plants