Probably the hardest job in an orchestra, but made to look so simple on the night!It's a bit ( lot) more than waving a stick around - when one conductor lost his baton, just about every violinist there offered him theirs!
You need to be conversant with each and every instrument and their foibles.
You need to be able to sight-read in the many transposing keys you'll find.
You need to be able to keep very good time.
You need to communicate clearly, often without using words.
You need to be able to look up from the score, and not lose your place in it.
To achieve some of these skills - there are plenty more - get hold of some instruments, and have at least a few lessons on each.
Start with small ensembles - quartets is a good place, and try to conduct in different ways - following the dots, but also putting your own dynamics etc. If the players follow faithfully, you know they're at least taking notice. Rather than you following them!
It's all very well pretending with youtube videos, but you're not actually conducting actively. More passively. Ask for a crescendo somewhere - is the orchestra going to respond? Of course not! However, it's good practice for reading the score - a few bars ahead of course - and getting used to looking away and finding your place again.
If you have scores - and they're not cheap - mark things like dynamics, repeats for certain parts, and such like, so you know exactly where each player should be.
Keep an ear on the tuning. Sometimes a section or an individual may be slightly off. If they are unaware, it's your job to sort out. Listening and looking at an ensemble, you should be able to hear and see which one plays a note too long, too short, to loud.
As a piano player, form a piano quartet and conduct from the piano, bringing in the players as needed, reading not only the piano part but the whole score. Start small and grow gradually. Good luck!
EDIT: almost forgot an important point - attend as many rehearsals as you can, as a spectator. (I used to enjoy listening to the rehearsals more than the concerts when at college), And take scores with you to any concerts .