Still gathering requirements...
You would need to ensure there are no funds in the company bank account as otherwise once the company is struck off you will lose access to these funds and they would go to the crown.
If you have set up a PAYE scheme then you would need to close this also and de-register for VAT if a registration was done.
The final thing from the company side of things is to notify HMRC Corporation Tax in writing that there has been no trade and therefore will be no Corporation Tax returns.
Then depending on your personal situation if you do not need to file a self-assessment tax return now and you have been sent a notice to complete one, you would just need to call HMRC and let them know of your change in circumstances and they can then update the record from their end.