I regularly remind numismatists that each coin in their collection should represent a significant purchase and stand on its own merit. Few coins ever become more important based on the company they keep. If you must accomplish completeness by filling openings in an album, leave insignificant purchases until the end and seriously contemplate their importance before paying good money to get them.
What I've always enjoyed and encourage others to try is building smaller sets within a larger set so if you decide to change direction what has been acquired is technically complete. Let me offer an example to illustrate this concept.
Let's suppose I decided to take on the ambitious project of building a complete set of Newfoundland Two Dollar gold coins. A quick glance at the catalog values proves this project is going to require time and patience. Is there some plan I can apply to my purchases so if the project becomes stalled, or I decide to move on to something different the coins I've acquired will remain significant additions to my collection instead of reminders that I didn't finish the set?
When reviewing what is needed to build a collection of Newfoundland gold one issue seems immediately interesting. Only one coin in the set carries a mintmark. By purchasing the 1882-H, in one swift move you have technically completed an entire collection. This particular coin is also one of the most affordable in the set and so acquiring it doesn't result in making a huge commitment to the project. What this purchase might also do is stimulate an interest in learning more about other coins made for use in Newfoundland by the Heaton Mint. Perhaps it would be possible to assemble a basic type set of these coins and once that is finished expand the collection to include other North American issues. Wait! I'm becoming distracted and losing focus! But it really doesn't matter when every coin is a significant purchase.
Getting back to our Newfoundland gold set, the next coin in the group that catches my eye is the 1865 issue. I will admit some personal preference influences this choice. Though they are often saved as curious novelties, I'm fond of first-year-of-issue coins simply for that reason. There is something special about being first. The 1865 coin is not only the first year of type but also the first gold coin made for a country. I find myself wanting to know why it was made. Were people in Newfoundland regularly using gold coins in commerce? What would such a coin purchase at the time? Who decided that 10,000 pieces, which together weighed a bit more than one sturdy person could comfortably carry, should be the total mintage? Why did it take five years before the next $2 gold piece was produced? Maybe it would be fun to build a type set of Newfoundland coins dated 1865? Excuse me for again straying from the original project. Investigating coins tends to do that to me. As long as each coin I select is obviously important and interesting to ME I'll never go far wrong.
My next choice for the Newfoundland gold set would be the scarce 1880 issue. This is another “stand alone” coin that is admired by many collectors, including those who have no interest in building a complete set.
To conclude, I hope I've reminded you how important it is to carefully consider the importance of every coin. Too often the combination of coins in a set tends to diminish the importance of some components. When all things are carefully considered, it's entirely possible for a rather plentiful coin to be far more interesting than one whose notoriety is primarily based on the number of examples available to collectors.