One of the single greatest training resources online right now is the Better Orienteering site (https://betterorienteering.org). This site has a huge collection of articles and media on every level of orienteering. Whether you need to work on fundamental skills, or need help understanding advanced techniques, the site has something for you.
For example - their page on basic techniques (https://betterorienteering.org/basic-techniques/) is a step by step breakdown of the processes that should be used by everyone to approach orienteering navigation in a methodical, organised way, in order to more reliably achieve good results.
In a similar vein, the following youtube playlist (by South London Orienteers) goes through the basic techniques we employ in orienteering:
The IOA have made a similar video going though the fundamental elements of orienteering from start to finish:
Jens Waechter (CorkO) gave an excellent presentation in Dec 2021 on how you might approach your Post-Race Analysis. Its important to ask questions of yourself after each event, so that you can identify your strengths and weaknesses, and in this talk Jens goes through how you might do this. Video of the talk is available below, and the analysis document he refers to can be found here
Here's a copy of David Healys Talk on Technical Training during the Winter