Where do I begin the process of putting in a packet for OCS?

Find your local accessions office and NCO's. They will likely help you drive that administrative process.

Next, go through your chain of command 1SG and Commander. At the very least you will need your Company Commander letter of recommendation and your CO will be signing off on validating your ACFT and H/W and that you are not flagged.

1) Your chain of command needs to be in on this, and are a central part to your success.
2) Accessions Office will be your administrative channel.

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As a reservist you are in a VERY POWERFUL position in that you are not anchored by an Active Duty daily work schedule. Meaning, you are going to be surprised by many things being thrown at you to add to your packet. Remember, you're not having to ask everyone in your chain for permission for the time to execute those actions. You just work it into your civilian schedule and make it happen.

What I can tell you from the perspective of someone who is an RA retiree but who knows two Guard officers, try for the RA OCS. One officer went that route the other went the expedited NG OCS camp and wished she had gone the RA OCS since it took her so long to get federal recognition. That federal recognition thing is alien to us RA folks but is a real concdern with the Army Guard. Both indicated the third route of the year long weekend OCS was by far the least preferred option. Apparently, in addition to the federal recognition issue the completion rate for the weekend OCS is abysmal.

If you have any interest in getting a masters a great way to commission is through ROTC.