Strmckr already gave you good advice on the order in which you can learn more advanced techniques. Some apps offer a practice mode in which you are given a specific grid that definitely needs that technique that you are trying to practice. One of those is my website sudoku.coach. The other one I know of is the windows software hodoku. Source: 11 months ago

On a Windows PC, Hodoku lets you input your own puzzle. You can just Copy and Paste this into the software:. Source: 12 months ago

Don't know about any sites but you can learn specific techniques in hodoku. Source: about 1 year ago

If I'm solving in Hodoku it's easy enough to switch to full notation (Options | Show All Candidates | click "no"), but my usual pencil/pen/eraser on paper takes slightly more effort. Source: about 1 year ago

Download/install Hodoku (Free, as in 'beer'; will run on Mac/Windows/Linux - it's a Java .jar file (also available as a Windows executable file). Source: over 1 year ago

I made an Escape from Tarkov quiz on jetpunk.com. Check it out and give me some suggestions on what to add or fix. Source: about 1 year ago

I gotchu with anything geography related: use jetpunk.com, they're great for working on geography. Catch me on there at NEGeo! Source: about 1 year ago

I absolutely do not think it has anything to do with socio-economics, because I'm from a low socio-economic background, as were lots of other kids at school, but we all knew where places in the world were and things about them. I do geography quizzes on jetpunk.com and get close to 100% on naming every single country in the world within 15 minutes. Source: over 1 year ago