What are some things and techniques I can do to minimize the time it takes for my apps/updates to be approved for the App Store? Do smaller updates generally take less time, and
App approval times will vary depending more on what else is going on, and can otherwise vary for no obviously predictable reason. I've seen a small update to a simple app take longer to approve than a new large app with lots of features.
Maximum app review times seem to be around the days that lots of other developers are submitting apps, near some major holidays, shopping seasons, or when Apple has just released some OS update, app service or new device. Shorter wait times can sometimes be had by avoiding these longer review time periods. There are services that track the number of new apps introduced per week. Look for the nulls.
Staying well away from any hint of violating any of Apple's App store rules or guidelines, or anything else that can be seen as controversial, also helps not getting hit by a long (additional time required) review time. Other factors seem to make less difference.
Take a look Apple review support
Once you've submitted your app for review, you can view its status in the My Apps section of iTunes Connect or on the iTunes Connect App for iPhone and iPad. Review times may vary by app. On average, 50% of apps are reviewed in 24 hours and over 90% are reviewed in 48 hours. If your submission is incomplete, review times may be further delayed or your app may be rejected. Once your app has been reviewed, its status will be updated and you will be notified.
Step 1:
Related to your project, note what is the third party libraries are involved and make a note what makes it rejected in apple store.
Step 2:
Make your code stable and keeping in mind about rejection points which you cant keep (i mean like really stable no warnings, no chance with wrong icons, no chance with mistakes).
Step 3:
Finally, then decide to send for review
That will at-least speed up your process. once you get rejected then its a bad, you have to really wait longer. (from experience saying)
You can request an expedited review in emergencies. I used it once and the update was available about one or two days later.
However, they say, the expedited review will only be granted in limited cases. So I wouldn't use it if not absolutely necessary.
You can request the expedited review in iTunes Connect. I think the option was on the detail page for an app which is 'Waiting for Review'. There was also a list, in which cases an expedited review can be granted.
I tried to use the expedited review for an app for a skistation, so it would be available before the winter season started and it was declined.
You need obviously a very good reason like a big security issue etc to get a expedited review.
I cannot post a comment yet, so I am posting this as an answer to your question based on my experience submitting new apps, as well as updates to existing apps in iTunesConnect.
Unfortunately there really isn't anything you can do to speed up the process, aside from fixing the issues in your app if it gets rejected, and re-submitting asap.
Apple allows you to request an expedited app review.
https://developer.apple.com/contact/app-store/?topic=expedite
Please note: If you're facing extenuating circumstances, you can request the review of your app to be expedited by completing the form below. Expedited reviews are granted on a limited basis and we cannot guarantee that every request will be approved.
I have personally used it twice. Once for a cosmetic issue in an app, which was rejected. Another time for a critical bug fix, which was accepted. I wrote a very detailed explanation of what my application did, what the bug was, why the bug was important to our (Mine and Apple's) customer.
One thing I have found is that free apps versus paid apps sometimes take different amounts of time.
For example I have a paid and free version of the same app. I submitted an updated for both one right after the other. First I submitted the free version, then I submitted the paid version immediately after. For some reason the paid version went into review, and was approved a day later, where as the free version is still waiting for review even know I submitted it first. I suspect that free and paid apps have different 'queues' or 'priorities' over at apple.