Unfortunately, there are no concrete answers to these questions, as each relationship, and each gift, is different. But in this post we'll try to provide at least a loose guide on some popular gift ideas.
Jewelry is more of a two way street than many people realize, as anything from a watch to a men's bracelet or ring can be classified in this category. Generally speaking, the appropriateness of this gift depends on its price and quality. Casual jewelry (say, under $100) is fine for an early birthday in the relationship, or perhaps a short-term anniversary (3, or possibly 6 months). Anything a bit pricier probably shouldn't come in the first year, or you may be looking a bit too serious.
Personal Interest Items
This is naturally an incredibly broad category, but one that sums up a lot of the types of gifts great for the early stages of a relationship. A personal interest item might be anything you notice your significant other loves: a popular bestseller for someone who loves to write, a Yankees hat for a fan of the team, a few films or CD's, etc. These aren't romantic gifts, but they show that you've noticed interests and preferences in the early months of a new relationship.
This may seem like an odd category to throw in, but believe it or not plenty of relatively young relationships reach the point at which these gifts are on the table. It's a bit of a delicate category, because you certainly don't want to come across as being too focused on sex - however, gauging your relationship appropriately, these can be very fun gifts for events like a birthday or Valentine's Day. It is, however, worth reading a bit at Adam and Eve, combing over item reviews and buyers' guides to make sure you pick something you'll enjoy as a couple. Another tip: don't make this the only gift you get, as that can send the wrong message. Use it as a fun accompanying gift to something a bit more meaningful.
Rather than separating this category into a batch of specifics - pricey necklaces, spa sessions, prime show tickets, etc. - the idea of expense is easier to work with. This is not to say that every gift is just about the money, but here's a helpful tip: if you think it seems too serious, or too heavy, it probably is. Something in this category is best saved for a 1st year anniversary, or any special occasion that follows.
This can be a temptation just about from day 1: nothing sounds more appealing than logging onto TripAdvisor and booking a getaway with your sweetheart! But, once again, too soon may mean too serious, at least for a getaway strictly as a couple. Booking a trip as a gift is a fairly serious, committed gesture, and is best saved for a time when your long term intentions have already been made clear. If you two are in agreement that you're going to give the relationship a real long term chance, book that getaway!