I usually made compromises when creating flightplans. The basic point in selecting the SID/STAR is the route. If you connect the departure and arrival airports in FSNAV, you will clearly see, how the route will look like generally. This will be the base for further selection.
For SID, I first search an intersection that is close to the airport (max 50nm), it is in my way to destination, there is possbile jetway from that point heading to the destination, and it is an exit point of any SIDs of that airport. It will take some long minutes to browse through the map, and the SID descriptions to found it. When you found that intersection, you found the SID group name, that is usually a town, or intersection name. After it, select a departing runway according to winds, or that is in use according to ATIS info, and then you can select the correct SID you need. It sounds maybe quite difficult, but it could be very easy too, when flying in Canada, for example

Selecting the STAR is similar. For first, find an intersection, that is an enter point of any STARs, and it fits to the route. Then select the runway, or the ATC will tell you the runway when you are near the airport. Then you can pick up the map of correct STAR for that runway, and prepare for landing.
Selecting the SID/STAR is usually your choice if otherwise the ATC not tell the procedure in use. If you make a clever selection, and ask a clearance for it, you will probable got it.