You can take a bemo from Mataram to Lembar Harbour. The fare should be about Rp 5,000, more if you are carrying a lot of luggage as it fills up the passenger carrying area, this is normal practice as the bemo's carry both people and goods including produce to the markets..
There are slow public ferries from Padang Bai (Bali) every hour. The trip normally takes four hours (but it can be considerably longer in poor weather) and costs Rp 35,000. This service runs 24 hours a day. It should be understood that this ferry has a poor safety record.
Arriving at Lembar Harbour do not let a porter take your bags unless you have negotiated absolutely what you will pay before he puts his hands on your bags. Best to avoid the service completely if possible as it can be fraught with complications over prices.
Getting from Lembar harbour
If you're arriving in Lembar and need transport, you'll find the Lembar bemo drivers hard bargainers.
Gili Islands. From Lembar Harbour you can take a shuttle bus service to Bangsal Harbour. Perama  will run shuttle buses from Lembar to Mataram and Bangsal, if there are enough passengers booked beforehand (Rp 60,000, min. 2 people). Depart : 6.30AM & 7AM - Return : 8AM. Or take a bemo from opposite the market in Ampenan up the west coast to Pemenang, from where you can walk or ride a cidomo (horse cart) to Bangsal Harbour. If you have plenty of time on your hands and want to save a couple of dollars, the cheapest way is to take a public bemo to Mataram (Rp 5,000), another to Ampenan and then another one to Pemenang/Bangsal (Rp 10,000), and then a cidomo (or walk) to Bangsal Harbour. From Bangsal Harbour, take the public ferry (Rp 8,000, 9,000, 10,000 depending to which of the Gilis you are heading to). Plan your trip to take in daylight hours only as the Bemo's normally do not run after dusk and can be reluctant to go past Mangsit at the northern end of Senggigi, this may require a set down and wait for another Bemo passing through Mangsit. It is best not too arrive in Bangsal too late as the last Koperasi Public boats leave in the early afternoon requiring the use of the slightly more expensive Shuttle boat in the late afternoon, or a Charter.
Mataram. You can take a bemo from Lembar Harbour to Mataram. The fare should be about Rp 5,000 to the Ampenan-Mataram-Cakranegara-Sweta area. A good option is to book ahead with Perama or another tourist shuttle company. Alternatively, metered taxis are available at the terminal or just outside the gates all day and all night. Typical fares are Rp 25,000 to Cakranegara, Rp 40,000–45,000 to Sengiggi.
Kuta. From Lembar Harbour the price to Kuta must be negotiated in advance, or you may insist the taxi driver uses a meter. Competition is fierce and porters will often place your luggage in a taxi prior to settling the price. Assertive behavior can insure you choose the taxi and the price that suits your needs.The taxi fare from Lembar to Kuta should be around Rp 250,000. Perama  will run shuttle buses from Lembar to Mataram, Kuta and Tetebatu, if there are two or more passengers booked beforehand (Rp 125,000 per person).
If you are leaving from Lombok, chances are high that someone will approach you and offer the ticket to Bali for same or cheaper than going the current rate of Rp 36,000 (March 2011). They'll also try to move you past official ticket offices (at the entrance gates of the harbour). It may be cheaper, however, you won't get an official ticket, or get only second part of it (the first one normally goes to the security on the pier). So, you may end up without a valid ticket and, if some security check happens, may have to pay again and suffer a lot of confusion. Just buy the ticket at the official ticket booth.
Bluebird (Lombok Taksi), ☎ +62 370 627000, . and the white coloured Express Taksi both have a radio despatch system and are equiped with meters which should be used by their drivers at all times, including all journeys originating from Lembar. Taxis can often be located near the main gate into the port area or you could try calling for one from inside the port area using a cellphone after disembarking.
Not a lot to see at Lembar other than the ferry docking area and the nearby sea port area. The surrounding countryside is quite attractive and the drive through to Mataram or the west coast is scenic and interesting with quite intensive agricultural pursuits lining the sides of the road.
This is really just a transit point, just try to get in and out as quickly as possible.
There are a few local warungs that cater to the port workers and transport drivers waiting to load their vehicles. Food and snack vendors also board the ships and make the crossing hoping to sell to the passengers during the voyage. A well prepared traveller may prefer to visit a supermarket or a trusted warung selling "nasi bungkus" or take away food and some drinks including bottled water before departing by road for Lembar. The seas can become rough so choose carefully.
Warungs near the dock area will have drinks available for sale but you may prefer to prepare yourself with some refreshments prior to departing to the dock. The ships do not provide clean drinking water so you will either need to bring your own drinks or purchase from vendors on the ferry. Alcohol is not sold on the ferry and the consumption of alcohol in public places is not condoned either in Lombok or Bali and that includes the sea in between.
There's little accommodation in Lembar and no advantage in staying.
Losmen Tidar, Jl Raya Pelabuhan, Lembar (about 300m along the road to the port from the junction with the main road from the city), ☎ +62 370 681444. If you do get stranded, Tidar has five rooms with fan and attached bathrooms, and a restaurant with a small menu of inexpensive Indonesian food.From Rp 50.000.
The ferries used on the run between Lombok and Bali do not conform to many Internationally recognised safety and operational standards.
It is prudent to keep alert and be aware of your position and situation whilst on board and make yourself aware of the positioning of life preserving equipment.
If inside the main cabin or below decks try to ensure you orient yourself to the layout of the ships decks and emergency exits especially if travelling at night.
You should maintain a clear head and use caution at all times when embarking and disembarking as the decks and ramps can be slippery and the passengers can at times behave in a chaotic manner especially when disembarking.
Be aware that heavy vehicles as well as cars and motorbikes are moving onto and off the ships at the dock and will using the same loading ramp as the passengers.
Be careful to keep track of your bags and watch out for pick pockets if in a crowd waiting to board or disembark.
There is a small Police post just inside the main entrance gate to the port area and a larger Polda national police base nearby.
Mobile phone towers ensure you're never out of touch. Telekomsel's Simpati SIM card has a reasonably good signal in the Lembar area and for a short distance out to sea. XL Comm SIM cards also provide coverage in the area. Coverage can be unreliable and inconsistent.