Just do the basics.
t-form valueable targets
get solar and lotus/picklets arround ur base
connect grid to ur teammate and DONT leave gaps even towards map border or leave a rigged chockepoint.
They want to fight ur homeground at/in ur base? Doubleclick solars turn em off (increases durability from 500 to 2.000!) let ur units walk/drag scynthes betwen solars, use com as bait if u have the skill/confidence and let the lotus etc. deal dmg (u want the enemy to have a negative trade)
dont go front with ur com (theres a reason why builders exist and u save a caretaker at ur factory) exept u know what youre doing.
If theres a strong scynthe spam player consider having 1-2 units near ur com in early game and stay within range of suitable defence with valueable units.
If they harass ur units, spread em out a little bit so the scynthes have to weaste some seconds by walking towards the next unit while getting shot by it. (ur goal is again to make sure the enemy to makes negative trades). As soon as the first attack hits react according to it and adjust the positions of the units.
Last thing is dont let them force you to play their game! Main damage of scynthe is mental warfare and guerillia tactics! No expand, no metal, hard time. Action and Reaction!