Some standard plays:
- Research to Education, GS Acoustics
- Research Metal Casting, GS Steel
- Research Physics and Steel, GS Gunpowder, use 4x Social Policies on Scientific Revolution to get Rifling
- (Babylonians only) As above, but use 3 Great Scientists to get Physics, Steel and Gunpowder for Rifles around turn 90
- Research Metallurgy and Chemistry, use 3x GS to get Fertilizer, Rifling and Dynamite
- Research to Banking for Forbidden Palace
Tech beelines primarily chase two things: units and Social Policies. Wonders (FP) and buildings (Biology for Hospital) are less common approaches. You should use beelines if you're a warmonger, or if you have a specific set of late SPs you want to run.
The Rationalism/Secularism/Freedom combination is very strong, as is Communism (in Order). Police State (Autocracy) lets you annex all of your conquests and makes their Happiness similar to India's UA, which can be quite helpful.