As others have mentioned showing them all all the features.
Here is how I go about it:
Firstly, explaining to them how iNaturalist works and how important the data is. Starting off by explaining that the app/website is an important place for researchers always gets people interested.
Here is an example: (Warning it is a bit of a bore for users who already use iNat. Also, feel free to use this as a “brain jogger” when explaining.)
Please be extra careful when pressing “agree” on identifications, especially the Computer Vision / Auto-ID ones. It is extremely important that you are careful with this because when an observation is research grade it becomes available to researchers and it can be frustrating and extra work for them if it is incorrect data. Also, when an observation becomes research grade it goes towards helping train iNaturalist’s Computer Vision, so incorrectly-identified RG can mess up iNaturalist’s map data and the Computer Vision for users who will use it later. Research grade isn’t a badge or something that you should even necessarily strive for. If it can’t be RG then it can’t be RG. When you click the Agree button, you are indicating that you believe it to be that species, based on your personal knowledge or research. It is important to remember that quite often most insects and spiders cannot be identified without microscopy. (The use of a microscope) That kind of independent identification is way, way more valuable than quickly clicking “Agree”, because it can be used to correct errors. I must admit that some of my oldest identifications were just carelessly agreeing without me actually knowing what was right or wrong, and this led me to quite a few misidentifications. I also often wanted everything to be brought down to species. I am more conservative. Don’t become my old self. I know animals and especially spiders can be really difficult to identify, and often specific, generic, or even familial identifications just can’t be made without examining the genitalia, a process which can be difficult and one which almost always involves killing the animal. A lot of the time, minor details must be located to confidently identify a particular spider, and some families can include members which can appear identical to another family and with other members appearing identical to a totally different family.
-My profile
In short, explain to them the importance of correct data. Next, show them your account and how you can simply take pictures and get CV suggestions, another thing that brings interest to users. Lastly, showing them the explore tab and how you can help identify observations are both points worth noting.
Projects, bioblitizes, etc. are all amazing features, but a bit of a mouth full to show, so when you are on the app doing a quick mention of annotations or projects might be useful to add when showing them how to add observations. If you are doing handouts or pamphlets those are things I would consider adding.
Most importantly, show them the fun aspects of it all!
Sorry, my comment is a bit of a long one lol, but I hope it helps!