Legend Numismatics has built more of the FINEST KNOWN Collections of true classic US coins than any dealer active today. We've built the FINEST EVER Half Dime collection. our signature FINEST EVER MS Trade Dollar Collection, and we have just finished building the FINEST EVER $3 GEM Proof Collection (just to pick three collections). There are many other great collection we've also enjoyed being major contributors too as well. No question we definitely are more qualified than most dealers to suggest to you how to build a great collection.
Do NOT feel you have to build a "registry collection." ANY great collection is an assemblage of phenomenal coins. It can be 5 MS66 colored Morgans, a mini set of 1900-1907 $2.5 in MS65, or even a Type Collection. Build a collection YOU want and YOU are comfortable with, do NOT feel you have to be involved in any race.
Pick a good dealer. You think you can do it on your own-WRONG! EVERY major world class collector has ALWAYS had a dealer with them the whole way. Pick a collectors name, Pittman, Bass, Eliasberg, EVERY MAJOR COLLECTOR has had a dealer working with them (today's great collectors are the same: Simpson and Pogue). A good dealer will not only help you get the "right" coins, but will save you from the bad ones. Overtime, they should also become you collecting buddy or partner. NOTE: this is NOT a self-serving suggestion (the chat room chimps are already destroying the message). Having multiple dealers shopping around for you does not make it any easier for you to find coins-it generally only costs you more. You really do want one dealer you can trust who WILL look out for your best interests.
The most critical thing when building ANY set-QUALITY. Stay true to this and do NOT buy holders. Our rule is: ALWAYS BUY THE BEST QUALITY YOU CAN AFFORD FOR THE GRADE. Also know EYE APPEAL is just as important. NEVER pass on a great quality coin because it is 10-30% too much.
Do NOT waste your money. We highly suggest you do NOT buy a "filler" just because you have a space. Usually it ends up a waste of money. ONLY buy the FINAL coin you want for your set no matter how rare a date is. If a dealer has a really rare coin that everyone needs, they will prefer cash, not a trade (those who want trades generally beat you up good on them). Sometimes it can also make a difference to a dealer that if you are known to write checks, you might get the coin offered to you first.