I got to 14kyu by playing and reviewing games, plus some some tsumego and pro game memorisation.
Then I decided to buy a couple of books: “Tesuji” and “Attack and Defense” - both from the Elementary Go Series. I also took a break for about a month.
Since then my rank has started to drop. Perhaps I have started to forget the basics? I don’t really know.
Any advice would be appreciated. Do I just keep playing and hope that I improve again?
Loosing stones when learning new things is pretty normal i guess. Just recently i lost about 3 stones just after finishing a book on attacking. I was just capping my opponents stones every single time and kept overplaying (but now I am one stones stronger than before and feel much more confident). Knowing more can sometimes make the game harder : maybe you see more possibilities but are not quite confortable enough to make the right choices so the result is worse than if you only saw one “average” possibility. In the end it will be benefitial : just keep playing, enjoy your games try the new things that you learned even if it means loosing a few games and you will understand when they work/don’t work. Also yeah make sure you keep doing the basic stuff correctly 
If you want a game just challenge me in correspondance (I am a bit busy atm so i can’t guaranty a tons of moves per day haha)
Also, payng to much attention to your rank may be detrimental, do not forget that ogs rank is very volatile, so a few stones difference doesn’t really reflect actual strength.
Yes. I keep overplaying and I’m also ignoring weakness and failing to protect cutting points.
Thanks for your reply. Maybe my drop in rank is a perfectly normal part of the learning process.
Don’t worry too much about your rank number. Volatility is natural when learning and experimenting with new things, and no rating system is perfect.
I would recommend ignoring your rank altogether. Just focus on enjoying games and trying to find the best moves.
I think it’s normal. I struggled when I started trying to learn new things but with a bit more playing practice and review it payed off. With me, when I learned about not playing things until necessary, to keep sente for example, I would be happy that I didn’t need to play X until my opponent played Y but then 100 moves later when it came to Y being played, I’d forgotten all about X… Lost many games like this but I guess in fact most of my play was at a higher level than before.
Well, if your last few games are any indication, it’s not because you’re approaching the game from a different angle after studying hard, I reckon the break was too long, so you’ve lost focus/sharpness. You’re making a lot of very uncharacteristic mistakes.
Advice is the obvious:
Thanks for the advice and the variations in those games.
I’ve started doing tsumego again, but not the pro games. Looks like 30 mins a day for each of these is the way forward.
I also need to take more time on moves. Apparently I am getting close to blitz speed even with plenty of time left on the clock. Maybe a checklist like the Clossi Approach might help?
On a more positive note, I did manage to beat two 9k players last month:
I probably focus more when playing better players.