Walking is the cheapest way because it is very pleasant in the cool air. If you choose to stay in a hotel at Dalat center, you can reach most of tourist attractions in a walking distance, especially for the famous Xuan Huong lake, coffee and food market.
Bus is another option but it is not very convenient because the routes stop at 5.30pm only.
Renting a bike is a nice idea, as you will be able to explore some natural sites around the city and exercise a bit. You can free your mind from pollution because air quality here is much better than that in big cities.
By Motorcycle -- Dalat is a good place to rent your own motorbike. The easiest places to find them are at the street side on Nguyen Thi Minh Khai street (between the market and the lake), estimated prices are under 10 USD per day. Choose the ones with the brakes and the horn still working, because you should use them all the way, especially when passing or on curves. Another good option if you are not confident in your driving skill is to get a motorbike with a driver for the day (about $1-$2 per hour, or fix a rate for the day and the destinations)
For some sightseeing which cannot be reached by foot, you can consider some ideas such as:
If you travel in a group, you can rent a car with a driver for about $35 per day for a four-seater, or $40 for a seven-seater, with most tour companies. For single and lazy travelers, simply jump in some joined groups where everything has been packed readily for you. Some tours even include off beaten track such as kayaking or trekking in the jungle for adventurous travelers so just ask for any available options which may seduce you most.