I'm lucky to live in Scotland so I save up my searches and visit a Scotland's People Centre for the day. There, for £15 I can view as many pages of search results and images as I can fit in for the day making it very cost effective. Especially so when searching for a David Smith.
My advice for people who have to rely on the website is to start their search as broad as possible to allow for location and spellings from being slightly out. However look at the number of results before clicking to use a credit. If there are a lot of results (more than 2 or preferably if more than 1 page) gradually narrow down the search parameters before selecting to view results.
Another tip I have is that registration district borders vary and an event may be registered in one place but for example but named as another as place of marriage on birth certificate of children or on census so have a map handy when searching to compare locations. while in England an event must be registered at the registration district where the event occurred in Scotland it can be registered at either the registration district it occurred or the one where the person was ordinarily resident. For example, my Dad died after being transferred to a hospital in Glasgow but his death was registered in the registry office that covers our village and shows up as such in the search results page. So keep this in mind when searching.