Self Study - General English
Where do I begin? How long should I spend? What activities should I choose?
My advice is to choose activites you enjoy doing in your own language and then do them in English. For example, if your hobby is ccoking, you could subscribe to a magazine in English, watch videos, buy recipe books in English etc.
Practise every day if you can, even if it’s only 10 minutes. Regular short sessions each day are far more effective than one long session from time to time.
Some useful sites to get started are listed below.
Gymglish

This site is subscription only but you can try it for free for 30 days.
They offer a top quality course which allows you to practise all the skills.
It’s an original fun interactive course based on the idea that daily practise is the best way to learn a language. Each lesson takes about 15 or 20 minutes to complete so it’s ideal for those who don’t have a lot of time.
It’s a step up from free applications such as Duolingo which are also a great way to improve.
https://www.duolingo.com
Coursera

The Coursera platform allows you to sign up for university courses all around the world. There’s a huge variety of courses available mostly running for about 6 weeks or so. They are generally video based (usually with the option of subtitles in English) so it’s another excellent way to hone your listening skills and build vocabulary. You can kill two birds with one stone: learn about a subject which interests you and improve your English at the same time.
The Guardian

Books
Reading in English is fantastic way to build your vocabulary. The golden rule is to read the kinds of thing you’d read in your own language. If you prefer non-fiction you could read autobiograhies or magazines which specialise in a hobby you have.
And if you like fiction, you are especially fortuante because novels and plays are a rich source of vocabulary and an excellent way to improve your English. The suggestions below are all classics but any contemporary novel wiil help you progress.
Other ways to practise
Watching TV series and films in English with English subtitles is probably the most powerful self study tool available. Apart from Netflix, HBO, Disney, Apple TV etc, you can also watch British TV by using a VPN.
When watching, I recommend you alternate between active and passive sessions.
Passive sessions involve watching a show without stopping just for enjoyment. Active sessions are when you stop the video and note down new vocabulary and a translation into your own language. If you write new words in the context of a sentence. you'll remember it more easily. When you re-read the words even months later, you'll often remember the exact scene it came from.
Practise watching shows in Enlgish without subtitles too from time to time without stopping the video. This can be frustrating at first but by removing the crutch of subtitles, you force your brain to process the information differently and will greatly improve your ability to understand gist.
Whatever you enjoy doing in your own language you’ll enjoy doing in English as well.
You can learn an enormous amount by yourself, partcularly with regards to listening and reading comprehension.
OET Self Study
Apart from numerous activities which you can find on the official OET website, I recommend the following.