You have made the decision of wanting to buy a home. Should you now go ahead and get pre-approved for a loan? Well, that is going to depend on how quickly you are ready to start shopping for a new home. If you are ready to view homes this weekend, and would be willing to submit an offer if you found the right home, than go ahead and get pre-approved ASAP.
On the other side of that you may want to take your time searching for the right home. It's quite possible that you haven't figured out where you want to live or whether you want a condo or a single family home. Once you get that squared away, and you've had an initial meeting with your Realtor®, than at that point you are ready to move forward with a pre-approval.
Pre-approval letters only last about 90 days. You can always renew them after 90 days, but why go through the hassle when you can just wait until you know that you are 30-90 days away from wanting to be a new homeowner.
If you have more questions with regards to the loan approval process, let me know and I can connect you with a good lender.