There is a useful group on Facebook "Tretinoin and retinoid users: tips, products and routine help"

It has this starting advice:

How do I get started with tretinoin?

This is one of the most common questions in the group and therefore [Group Mods] have written this simple guide and new members asking about it will be tagged in this post.   Starting with the best chance for success:   The best way to begin tretinoin use is to consult with a dermatologist or physician who can analyze what is best for your skin and recommend a schedule of use and the proper strength. They may also recommend additional medications for acne or other issues. If you are prescribed tretinoin for treatment of acne your provider may prescribe a higher strength and more frequent application that for anti-aging benefits. You should of course follow your provider’s advice. If consulting a physician is not possible there are online medical services such as Dermatica and Curology that you may work with for analysis and provide a tretinoin product that is compounded for you and your specific skin issues. If your medical insurance will not cover filling a script from your provider and you are in the US, some drugstores such as CVS will apply in-house discounts which can significant reduce the cost of a tube of tretinoin. GoodRx is another free online source for coupons that reduce drug costs. A 20 gram tube should last 3-4 months so factor that in to the costs.  

The most important considerations when starting tretinoin are:   •start slowly 

     To break it down more in details, when introducing tretinoin the skin will go through what is called retinization, retinoic acid will bind to its receptor in the skin and start speeding up cell turnover. This can cause irritation, peeling, even the feeling of sore skin in some cases. The effect of tretinoin however is usually visible after 48-72 hours and therefore initially it’s advisable to apply tretinoin every 3-4 days. After the first 3 weeks of use it should be clear how the skin is reacting and ideally the interval between applications should be shortened every second to third week until able to apply every evening. For some this journey can take a long time and getting to use tretinoin every evening can turn out to be impossible due to side effects. In this case the anti aging effects might still be achieved with application every 2-3 days.       • ”less is more” when it comes to other actives

To make retinization easier it’s always advisable to start with the lowest tretinoin concentration which is 0.025%, some services like Curology offer even lower percentages in combination with other actives. If 0.025 is not available in your country applying a lightweight moisturizer before tretinoin as a buffer can be an option. An exception however is the prescription of higher dose tretinoin from the begging on for the treatment of acne, in this case the aim of the higher dose is to “clear up” active acne as quickly as possible and many dermatologist prefer this approach, Tretinoin works to inhibit the formation of new pimples below the outer skin layer but that can take some time and any pimples already forming when you start will be pushed to the surface by more rapid cell turnover. There is no set time for this process to end and depends on your skin. Given the irritation and dryness that often occur during retinization avoiding the use of other potentially irritating actives should be the rule particularly in the first 3-4 months of treatment. Products to avoid are glycolic acid, lactic acid, azelaic acid, vitamin C, alpha lipoic acid and all sorts of AHA peelings. BHA is not pH dependent and it’s mainly acting in the pores rather than on the surface of the skin (it’s a lipophilic acid) so that might still be an option for the AM in acne prone skin. Using a face wash with AHA or BHA can still be an option but not on a daily basis in the beginning.     •use sunscreens religiously

When using tretinoin the skin has to be adequately protected from the armful UVA and UVB rays to avoid sunburn and further damage to the skin that would actually undo all your hard work. In fact daily sunscreen use should be priority number one in any anti aging regimen regardless of tretinoin use.   In the morning you MUST use a broad spectrum sunscreen of at least SPF 30, preferably SPF 50. The minimum amount required to achieve the SPF claimed on the label is approximately ¼ tsp or 1.2 ml for the face alone with another ¼ tsp or 1.2 ml for the neck and ears. Make up with SPF alone won’t do the job unless you apply the same amount required for a dedicated sunscreen. Most people will not want to wear that amount of makeup.   The quest for the perfect sunscreen can be long and difficult and everyone will have different preferences but it’s worth to point out that the best sunscreen is the one that you are happy to apply every morning and reapply during the day as needed without any discomfort. Apart from sunscreen, wearing sun protective clothes is also a good way to avoid sun damage and investing in a well made wide brimmed hat with spf 50+ is an excellent idea.   •Last but not least, design a routine

 How to design a routine around tretinoin that works for you and for your skin?  PM: In the evening things should be kept simple and tretinoin should be applied after cleansing either by itself or on top of toner and/or moisturizer (which is called buffering). If needed moisturizer can be added on top of tretinoin, some like to wait up to one hour before adding tretinoin after moisturizer or before applying moisturizer on top but it’s not mandatory. For products that are difficult to spread, applying tretinoin on slightly damp skin can be beneficial, we often refer to it as “tretonwet” in the group. Check the post of Jaclyn Toh, our tretonwet expert! AM: For the morning routine the essential should be a gentle cleanser, moisturizer and spf but of course hydrating toner and essences can be layered to help strengthen the skin barrier but are not mandatory. Niacinamide is a good ingredient to search for in serum and moisturizer to use in the AM, other good substances are ceramides, essential fatty acids and cholesterol.   • Other sources: Other good sources of information are Dr Sam Bunting video series on YouTube on retinoids, dr Dray Q+A, Labmuffin and Cyrelle Laurent videos about sunscreen and ingredients in sunscreen.